
Class 
Book 



Kii 



Aa 



d. 



Copyright N?. 



COPYRIGHT DEPOSIT. 



PRACTICAL ELECTRICITY 



(IN HAND BOOK FORM) 



This manual, formerly known as Sloane's ''Electrician's 
Handy Book " is a popularly written treatise upon almost 
all phrases of electricity, with the simplest of mathematics, 
and may properly be termed an Elementary Text Book 
of Electricity. 

INCLUDES 

The Theory of the Electric Current and Circuit, Electro-Chemistry, 
Primary Batteries, Storage Batteries, Generation and Utilization of 
Electric Power, Alternating Current, Armature Winding, Dynamos and 
Motors, Motor Generators, Operation of the Central Statioa, Switchboards, 
Safety Appliances, Distribution of Electric Light and Power. Street 
Mains, Transformers, Arc and Incandescent Lighting, Electric Measure- 
ments, Photemetry, Electric Railways, Telephony, Bell- Wiring, Electro- 
plating. Electric Heating, Wireless Telegraphy, Etc. Etc. 

f BY 

xfb'GONOR SLOANE, A. M., E. M., Ph. D. 

Author of "Electric Toy Making", "Electricity Simphfied ", etc. 




Third Edition Fully Illustrated by 556 Illustrations 

NEW YORK 

THE NORMAN W. HENLEY PUBLISHING CO. 

132 Nassau Street, 

1913 



i^ 



^"V> 



Copyrighted 1913 and 1905 



BY 



The Norman W. Henley Publishing Co. 

Also entered at Stationers' Hall Court 
London, England 



All Rights Reserved 



• 


^ 
^ 

^ 


^^sf-O 


©CI.A350S86 





PREFACE. 

After many months of preparation, the Electricians' Handy- 
Book is finished and given to the reader. The work of covering 
the whole immense field of electrical engineering from early 
days to the present time would certainly be an endless one; the 
work of writing the present book has been lightened by the fact 
that the progress of electrical science in its practical aspect has 
been in the direction of the survival of the fittest. This ten- 
dency has had the effect of removing from the field of engineering 
many most ingenious devices, whose consignment to oblivion 
might be a subject for regret. But this disappearance of the 
old makes the amount to be described and learned less, and there- 
by lightens the labor of author and student. 

It is fair to say that the development of electrical engineering 
is largely in the direction of simplification. In early days re- 
sults inferior to those attained in the present era were secured 
by the use of apparatus more elaborate than that which is now 
employed. The evils of complication have long been recognized, 
and the trend of invention has been to avoid it. One of the earliest 
objects of the inventor was the production of an arc lamp with- 
out mechanism; the results of these efforts have completely dis- 
appeared from view, and the greatly simplified arc lamps of the 
present day are their successors. 

The same history can be traced for other branches of the 
science. Quantities of the most ingenious inventions are no 
longer in use, simpler machinery has taken their places. For elec- 
trical engineering is nothing if not practical, and sentiment has 
no part in dictating what shall survive and what shall be for- 
gotten. 

Something remains to be done in the elucidation of the theory. 
The very name of the science has never been adequately de- 
fined, although the working theory has been developed to a high 

3 



4 ELECTRICIANS' HANDY BOOK. 

degree of perfection. The greater general familiarity with the 
mere names of things electrical makes the subject seem less mys- 
terious than formerly, when the words "ampere," "volt," and 
the like were rarely heard outside of a college. This should not 
induce the student to feel that his path is any shorter than was 
that of his predecessors. It is if anything a much longer one, 
made a little easier by the fact that it is now a better-marked 
one. But he has more to learn than had his predecessors, and it 
m.ust be more exactly learned. The modern science cannot be 
trifled with. 

This book is sent on, its way with the fullest sense of the diffi- 
culties involved in its preparation. It is hoped 'that it will meet 
with a favorable reception. In its writing the literature of the 
science has been freely used, and such classics of engineering 
literature as Miller's "American Telephone Practice," Crocker's 
"Electric Lighting," Abbott's "Electrical Transmission of Energy," 
and other works have been consulted at length. The author's 
thanks are also due to the General Electric Company, the Leeds & 
Northrup Company, and to many others for assistance most kindly 
rendered. Any suggestions which would be available for future 
editions of the book will be gladly received from readers. 

THE AUTHOR. 



CONTENTS. 

CHAPTER I. 

MATHEMATICS. 

Electrical Calculations — Algebra — Direct and Inverse Proporticn— 
Percentage — Fractions — Compound Fractions — Inverted Addition and 
Subtraction — Multfplication and Division — Squares of Numbers — Cancela- 
tion — Powers of Ten or Exponential Notation — Logarithms — Angular 
Measurements — Radian System of Angular Measurement — Trigonometric 
Functions — Numerical Values of Circular Functions — Greek Letters — 
Useful Constants — Torque — The Dynamometer — The Prony Brake — Lumi- 
niferous Ether 17-40 



CHAPTER II. 

ELECTRIC QUANTITY AND CURRENT. 

Electric Quantity — Storage of Electric Quantity — Condensers — Charg- 
ing — Meaning of Quantity of Electricity — Earthing a Condenser — Capa- 
city of Condensers — Single Surface Condensers — Unit of Quantity — The 
Storage of Quantity of Electricity — Capacity — Dielectrics — Specific In- 
ductive Capacity or Inductivity — Examples of Capacity — Microfarad — 
Current and Rate Units — Conductors and Non-Conductors — Ether Waves 
Produced by Electricity — Action of a Conductor — Time Required to Pro- 
duce a Current — Production of Current — Current, Amperes, and Coulombs 
— Current Strength or Intensity — Analogy for the Ampere — Speed of a 
Current — Arrival Curve — Direction of a Current — Memoria Technica — 
Field of F'orce and Lines of Force Due to Current — Electromotive Force 
— Production of Electromotive Force — Dynamic and Static Electricity — 
Electromotive Force and Energy — Conservation of Electricity — Electro- 
motive F'orce and the Static Charge — Electromotive Force in Thunder 
Clouds — Electromotive Force the Cause of Current — Drop of Potential — 
Analogies of Drop of Potential — Electromotive Force and Difference of 
Potential — Voltage 41-62 

CHAPTER III. 

THE ELECTRIC CIRCUIT. 

Ttie Electric Circuit — Constitution of a Circuit — Condensers in a Cir- 
cuit — Open and Closed Circuits — Circuits Without Appliances — Appli- 
ances and Generators in Circuits — Electrolytic Conductors — Actions of a 
Circuit — Parallel and Shunt — Series — Series Multiple — Multiple Series — 
Series and Parallel — Outer Circuit — Short Circuit — Conductibility, Con- 
ductance, and Conductivity — Resistance — Resistance and Energy — The 
Ohm — Internal and External Resistance — Circuit Without Resistance — 
Electrolytic Conduction 63-73 



6 ELECTRICIANS' HANDY BOOK, ' 

CHAPTER IV. 

ohm's law. 
Three Elements in a Circuit — Ohm's Law — Examples of Ohm's Law — 
Five Forms of Ohm's Law — Importance of Ohm's Law — Power — Examples 
— Constant Current Circuit — Constant Potential Circuit — Drop and Pall 
of Potential — R. 1. Drop and Counter E. M. F. — Examples of Power 
Calculations — Calculation of Resistance of Parallel Circuits — Examples 
of R. I. Drop Calculations — Example of Counter Electromotive Force 
Drop Calculations — Kirchhoff's Laws — Conductance and Cross-Sectional 
Area of Conductors — Circular Mil System — Application — Area of a Cir- 
cular Mil — Examples — Wire Gauges — American Wire Gauge 74-87 

CHAPTER V. 

ELECTRO-CHEMISTRY. 

Water Decomposed by the Coulomb — Hydrogen Liberated by the 
Coulomb — Proportion of Hydrogen to Oxygen — Atomic Weights and Chem- 
ical Equivalents — Electro-Chemical Equivalents — Current Strength and 
Chemical Decomposition — Sammary — ^Example — Electromotive Force in 
Chemical Decomposition — Voltage Calculation 88-93 

CHAPTER VI. 

PRIMARY BATTERIES. 

The Primary Battery Cell — Three Constituent Parts — Simple Batteries 
■ — 'ISomenclature — Negative and Positive Plates — Cell, Couple, and Pair — 
Exhaustion and Polarization — ^Local Action and Amalgamation — Volta's 
Battery — Volta's Pile or the Galvanic Pile — Wallaston's Battery — Hare's 
Calorimeter — Zamboni's Pile — Modern Batteries — Smee's Battery — Iron 
Negative Plates — Aluminium Negative Plates — Grove's Battery — Carbon 
Negative Plates — Moving Electrodes — Bunsen's Battery — Modifications of 
Bunsen's Battery — Gibbs' Battery — Poggendorff's Battery — Modifications 
of Poggendorff's Battery — Fuller's Mercury Bichromate Battery — Cam- 
acho Cascade Battery — ^Baudet Siphon Battery — Radiguet Battery — 
Grenet's Battery — Dip Batteries — Partz's' Battery— Depolarizing Mixtures 
and Exciting Solutions in Batteries of the Poggendorff Type — Mixtures 
of Sulphuric and Nitric Acids — Potassium Bichromate Solutions — The 
Daniell Battery — Modifications of Daniell's Battery — Sand Type of Dan- 
iell's Battery — Gravity Battery — Meidinger's Battery — Modification of the 
Gravity Cell — Caustic Alkali Batteries — Modifications of the Lalande and 
Chaperon Battery — Ammonium Chloride Batteries — Dry Batteries — Ar- 
rangement of Batteries 94-124 

CHAPTER VII. 

STORAGE BATTERIES. 

The Primary Battery — Action of a Storage Battery — Regeneration — 
Grove's Gas Battery — Requirements of a Storage Battery — Function — 
Plante's Battery — F'orming — Storage Capacity — Faure's Battery — The 
Faure-Sellon-Volckmar Battery — Chemical Action — Resistance — Gould 
Storage Battery — Flelios-Upton Battery, Philadelphia — American Stor- 
age Battery — Crompton-Howell Battery — Pasted Plates — B. P. S. Battery 
— Chloride Battery — Tudor Battery — Suspended Plates — Other Types of 
Pasted Plates — Copper Storage Batteries — Zinc Acid Storage Batteries — ■ 
Waddell-Entz Battery — Edison's Storage Battery — The Discharge — Dis- 
charge on Open Circuit — Manufacturer's Data — Determination of Dis- 
charge — The Charge — ^Specific Gravity Variation of Electrolyte — Hydro- 
meters — Gassing — Gas Evolution — The First Charge — Automatic Cut-off 
or Circuit Breaker — English Rule for Charging — Overcharge — Prevention 
of Sulphating — Short-Circuiting of Single Cells — Sediment — Buckling — • 



CONTENTS. 



Disintegration — Setting up a Battery — Preparing the Electrolyte — Impuri- 
ties in the Electrolyte and Tests — Indications from Gassing — -Cadmium 
Plate — Connections for Charging from Lighting Circuits — The Polarity 
of the Circuit — Taking Out of Service — Cells — Insulation of Cells — Mak- 
ing Battery Connections — Practical Notes — End Cells — Counter Electro- 
motive Force Cells — Floating Battery — Charging Plant Operation. 125-166 

CHAPTER VIII. 

THE FIELD OF FOKCB. 

The Field of Force — Ether and Current — Detection of the Field — Lines 
of Force Produced by a Curved Conductor — Motion of a Conductor in a 
Field of Force — Direction or Polarity of Lines of Force — Memoria Tech- 
nica for Lines of F'orce — ^Utility of the Conception of Lines of Force — 
Density of a Field — The Magnetic Circuit — Energy and the Magnetic Cir- 
cuit — Counter and Forward Electromotive Force — Building up the Field 
of Force — Potential Energy of the Field of Force — Energy and the Field 
of Force — Nature of the Magnetic Circuit — Permeability and Permeance 
— Iron and the Field of Force — Saturation — Three F'actors of the Mag- 
netic Circuit — Magnetic Forc?s — Ampere Turns — Field Density — Permea- 
bility — Saturation of Iron — No Insulator of Magnetism — The Gauss — 
Reluctance and Reluctivity — Synonyms for B, H, and mii — B and H 
Curves — ^Interpretation — Practical Considerations — Permeability Curves — 
Soft Steel in Dynamos — Annealing — Determination of Curves — Relation 
Between Ampere Turns and Lines of Force — Leakage of Lines of Force — 
Stray Field — Permeance of a Magnetic Circuit — Hysteresis — Residual 
Magnetism — Hysteresis Curves — Loss of Energy Due to Hysteresis — 
Hysteretic Constant 167-187 

CHAPTER IX. 

MAGNETS. 

The Electro-Magnet — Tractive Force of the Electro-Magnet — Spreading 
of Lines of Force — Illustrating Lines of Force About a. Magnet — Spiral 
Electro-Magnet — U-Shaped Electro-Magnets — Annular Chambered Magnet 
— Electro-Magnetic Tractive Power — Multipolar Magnets — Various Arma- 
tures — The Natural Magnet — The Permanent Magnet — Action of Magnet 
Poles on Each Other — Making Magnets by Single Touch — Making Mag- 
nets by Double Touch — Making U-Shaped Magnets — :\Iagnetizing by Coil 
and Electro-Magnet — Steel for Magnets — Preservation of ^Magnets — Ex- 
amples of Permanent Magnets — Polarized and Magnetized — Constancy of 
Magnetism — Mutual Action of Currents — Ampere's Theory of Magnetism 
— ^Memoria Technica — Ampere's Theory of Terrestrial Magnetism — Attrac- 
tion and Repulsion of Magnetic Poles — Action of a Current on the Magnet 
— Ampere's Rule — ^Right-Handed Screw Law 188-204 

f 

CHAPTER X. 

INDUCTION. 

Electro-magnetic Induction — Threading, Interlinking, and Cuttting Lines 
of Force — Induction — Conditions for Inducing Electric Energy — Examples 
of Interlinking — Motionless Conductor in a Field of Force of Varying 
Density — Energy Relations — Fields of Force in Practice — Direction of 
Current Induced by Cutting Lines of Force — Two Systems of Induction 
■ — Generator Without Motion — Examples of Induction — Telephone Re- 
ceiver a Dynamo — Laws of Induction — Faraday's Law — Fleming's Rule 
— ^Ampere's Rule Adapted to Induction — Clerk-Maxwell's Rule— Lenz's 
Law — Example of the Application of Lenz's Law — Foucault or Eddy 
Currents — Variations in Impressed Electromotive Force — Direction of 
Currents Induced in Coils 205-217 



8 ELECTRICIANS' BANDY BOOK. 

CHAPTER XI. 

DIRECT-CURRENT GENERATORS AND MOTORS. 

Dynamo-Electric Generators — Interchangeability of Dynamo and Motor 
— Varieties of Dynamos — Elementary Idea of an Alternating Current 
Dynamo — Collecting or Slip Rings — Brvishes — Elementary Idea of a Di- 
rect-Current Dynamo — Increasing the Electromotive Force by Increasing 
the Turns — Increasing the Electromotive Force by Adding an Armature 
Core — Armature and Core — Field Poles — Open-Coil Armatures — Spindle 
or H Armature — Closed Coil Direct-Current Armature — ^Cutting Lines of 
Force Without Change in Number of Interlinking Lines 218-224 

CHAPTER XII. 

DIRECT-CURRENT ARMATURE WINDING. 

Armatures — The Pacinotti Armature — The Gramme Ring — Modern 
Types of Closed-Coil Armatures — Commutator Connections of Ring Arma- 
ture — Cores of Ring Armatures — Permeance of the Ring Core — Idle Wire 
— Circuit in a Ring Armature — Open-Wound F'our-Part Ring Armature — 
Mounting of a Ring Armature — Multipolar Ring Armature — The Drum 
Armature — Action of the Drum Armature — Drum Armature Winding — 
Simple System of Armature Winding — Eight Conductor Drum Armature 
— Twelve Conductor Bipolar Armature — Sixteen Conductor Bipolar Arma- 
ture — Winding Tables — Windings for Multipolar Fields — Eighteen Con- 
ductor Four-Pole Armature — Circular Development — Commutator Connec- 
tions — Wave and Lap Winding — Wave Winding — Lap Winding — Develop- 
ment of Commutator Connections — Development of Field Poles — Develop- 
ment of Current Induced — Straight Developments — Winding a Drum Arm- 
ature — General Considerations in Laying Out Drum Armature Windings 
— Single Layer Winding for Bipolar Field — Double Layer Winding for 
Bipolar Field — Commutator Connections — Multipolar Windings — Multi- 
polar Lap Windings — Nomenclature for Drum Armature Windings — 
General Formulas — Bipolar Winding by Formula — Multipolar Winding 
by Formula — Lap Winding 225-249 

CHAPTER XIII. 

THE DIRECT-CURRENT GENERATOR. 

The Magneto Generator — The Modern Multipolar Dynamo — Field Wind- 
ing of Dynamos — Series Winding — Action of Series Winding — Shunt Wind- 
ing — Action of Shunt Winding — Compound Winding — Short Shunt Com- 
pound Winding — Long Shunt Compound Winding — Action of Short-Shunt 
and Long-Shunt M^inding — Self-Regulation of Compound Wound Dynamos 
■ — Characteristic Cur/es — Over-Compounding — Example of Compound 
Winding Calculation — Excitation of Field Coils in Compound Dynamos — ■ 
Effect of Independent Excitation of Shunt Coil — Disconnecting or Open- 
ing the Shunt Coil — Separate Excitation of Shunt Coil — Exciting Series 
Coils from Main Circuit — Separately-Excited Generators — Action of the 
Separately-Excited Dynamo — Regulation of Separately-Excited Dynamos 
and Magnetos — The Separate Circuit Dynamo — Separately and Self-Ex- 
cited Dynamo — Multipolar Dynamo Connections — ^Conventional Repre- 
sentation of Machines 250-264 

CHAPTER XIV. 

ARMATURE REACTIONS. 

Armature Polarity Due to its Windings — Action of Field Poles on 
Armature Core — Field Distortion — Armature Reaction Diagrams — Varying 
Densities of Field — Neutral Points — Brush Adjustment — Demagnetizing 
Turns — ^Reduction of Field Density — Action of the Demagnetizing Turns 
— Dead Turns — Spurious Resistance — Eddy or Foucault Currents — Eddy 



CONTENTS. 9 

Currents in Armature Cores — Eddy Currents in Core Disks — Eddy Cur- 
rents in Pole Pieces — End Leakage of Lines of Force in Armature — Eddy 
Currents in Conductors 265-272 

CHAPTER XV. 

CHAEACTEEISTIC CUEVES. 

Characteristic Curves — Horse-Power Lines — Types of Characteristic 
Curves — Drooping Characteristic — Interpretation of Characteristic Curves 
— Data for External Characteristic Curves — Data for Total Characteristic 
Curves — Drawing Characteristic Curves — Internal Characteristic — Termin- 
ology of Analytical Geometry — Line of Ohms — General Notes on Char- 
acteristic Curves — Critical Current — Shunt Wound Dynamo Character- 
istic — Critical Point of Shunt-Wound Dynamo — Total Current Character- 
istic in Shunt Dynamo — Total Characteristic of Shunt Dynamo — Ohm- 
Volt Curves 273-284 

CHAPTER XVI. 

THE DIEECT-CUEEENT MOTOE. 

Direct-Current Electric Motor and Torque — Reversibility of Dynamo 
and Motor — Generator and Motor Connected — Counter Electromotive 
Force — Action of Counter Electromotive Force — Relations of Speed of 
Generator and Motor Connected — Counter Electromotive Force and the 
Armature 285-288 

CHAPTER XVII. 

OPEN-COIL GENEEATOES, 

Open Coil Armature Winding — The Brush Dynamo — Brush Dynamo 
Construction — The Thomson-Houston Armature — Homopolar, Acyclic or 
Unipolar Dynamo — Relation of Size and Output of Dynamos — Manu- 
facturer's and Thompson's Rules — Deduction of Thompson's Factor — The 
Sixth Power Rule 289-296 

CHAPTER XVIII. 

GENEEATOE AND MOTOE CONSTEUCTION. 

Disks for Smooth Surface Armature Cores — Disks for Grooved Armature 
Cores — Formed Coils — Wire Winding — Insulation of Conductors — Core 
Grooves and Wooden Wedges — Winding Armatures with Formed Coils — 
Pole Armatures — Disk Armature — Commutator Construction — Position of 
Commutator — Brushes and Brush Holders — Tangential Brushes — Trim- 
ming Metal Brushes — Radial Brushes — Position of Opposite Brushes — 
Brush Rigging — Relation of Depth of Air Gap to Sparking — Field Magnet 
for Multipolar Dynamos — Laminated Field Magnets — Sectional Laminated 
Field Magnets — Details of Multipolar Field Windings 297-315 

CHAPLER XIX. 

THE ALTEENATING CUEEENT. 

Alternating Electromotive Force — Cycle, Wave and Frequency — Elec- 
tromotive Force and Current Curve — Production of Alternating Electro- 
m-otive Force and Current — Length of a Wave — Form of Alternating 
Electromotive Force and Current — Length of Wave and Frequency — ■ 
Cause of the Form of Alternating Electromotive Force and Curi-ent — 
Alternating Electromotive Force and Current Curves — Drawing the Elec- 
tromotive Force and Current Curves — Degree System — The Sine Curve- 
Generating Circle — Interpretation of the Generating Circle — Rate of 



10 ELECTRICIANS' HANDY BOOK. 

Change — Graphic Representation of Rate of Change — Radius Vector and 
Resultant — Vector Diagram of a Sine Curve — Phase, Lag and Lead — ■ 
Angle of Lag and Lead — Quadrature and Opposition^Basis of Lag and 
Lead — Average Values — Effective Values — Calculation of Effective Values 
■ — F'orm Factor — ^FormuIas for Effective Values — Power Factor — Qualities 
of a Circuit — Resistance — Reactance — Inductance — Inductance and the 
Henry — Electromotive Force in an Alternating Current Circuit — Counter 
Electromotive Force — Forward Electromotive Force — Counter and For- 
ward Electromotive Force in an Alternating Current Circuit — Turns of a 
Circuit and Inductance — Reactance of Inductance — Ohmic Equivalent of 
Reactance of Inductance — Inductance Reactance in Subdivided Conductor 
— Capacity — Reactance of Capacity — Ohmic Equivalent of Reactance of 
Capacity — Impedance — Electric Resonance — Causes of Lag and Lead — 
Summation of Alternating Quantities — Composition of Resistance, Induct- 
ance and Capacity — Multiplication of Alternating Quantities — Power 
Curves — Two-Phase Current — Three-Phase Current 316-347 



CHAPTER XX. 

ALTERNATING CUEBENT GENEEATORS. 

Generation of Alternating Current — Sjngle-Phase Armature — Multipolar 
Construction — Grouping of Windings — Principle of Alternating-Current 
Armature Winding — Drum-Armature Connections — Elementary Four-Pole 
Single-Phase Armature — Single-Phase Wave and Lap Winding — Ring 
Winding for Alternating Current — Conventional Representation of Col- 
lecting Rings — Pole Single-Phase Armature — Rotor and Stator — Inductor 
Alternator — Disk Windings — Two-Phase Winding — Three-Phase Winding 
— Six-Wire Connection of Three-Phase Alternator Winding — Y or Star 
Connections — Delta or Mesh Connection — Line Connections — Neutral Wire 
in the Y System 348-362 

CHAPTER XXI. 

ALTERNATING CURRENT MOTORS. 

The Induction Motor — The Rotary Field — Magnetic Needle in a Rotary 
Field — Armature in a Rotary Field — ^Three-Phase Induction Motor — In- 
duction Motors — Rotary and Revolving Field — Starting Torque — Squirrel 
Cage Armature — Starting Resistances — ^Starting Compensator — Lenz's 
Law and the Induction Motor — Construction of Induction Motors — The 
Synchronous Motor — Condition of Operation — Single-Phase Synchronous 
Motor — Synchronous Polyphase Motor — Self-Starting Synchronous Motor. 

363-374 

CHAPTER XXII. 

TRANSFORMERS. 

Basis of Transformer Construction — Object of a Transformer — Choking 
■ — Limitations of a Transformer — The Principle of a Transformer — Shell 
or Jacket Type of Transformer — Step-Up and Step-Down Transformers 
— Ratio of Transformation — Shell-Type Transformer — Core Transformers 
■ — Disk-Wound Transformers — Pancake Coils — The Autotransformer — 
Action of the Transformer — Heat in Transformers — Oil Cooling — Water 
Cooling — Air Blast Cooling — Details of Transformer Construction — Shell- 
Type Transformers — Disk Winding — Constant Current Transformers — 
Oil for Transformers — Insulation in Transformers — Direct Current from 
Alternating Current — Rotary Converter — Use of the Rotary Converter — 
Principles of Construction — Relation of Voltage and Current — ^Rotary 
Converter in the Three-Wire System — Starting a Rotary Converter — ■ 
F'unctions of a Rotary Converter — The Rectifier — Operation of Trans- 
formers 375-396 



CONTENTS. 11 

CHAPTER XXIII. 
MANAGEMENT OF MOTORS AND DYNAMOS. 

Starting Motors — The Starting Boxes — Magnetic Release Starting Box 
— Starting-Box Connection — Clianging Voltage — Motor Transformer — 
Action of tlie Motor Transformer — Step-Down and Step-Up Transformer — 
Motor Transformer I*ractice — Ttie Economy of Motor Transformers — 
Parallel Coupling of Dynamos — Parallel Coupling of Shunt Dynamos — 
Parallel Coupling of Compound Dynamos — Shunt-Wound Machines in 
Series — Reversal of Direction of Armature Rotation — Polarity Tests — 
Alternators in Step — Synchronizing — Regulators or Boosters — Booster 
Connections — Hand Regulation of Boosters — Automatic Regulation of 
Boosters — Booster Construction — Motor Dynamos as Boosters — Compensa- 
tors — Floating Battery — ^Booster and Storage Battery Connections — ■ 
Crushers — The Crocker-Wheeler System of Speed Control — Accidents to 
Motors 397-415 

CHAPTER XXIV. 

CARE OF DYNAMOS AND MOTORS. 

Reversing the Direction of Current — Stopping a Machine — Too High 
Speed — Loss of Magnetic Polarity — Wrong Polarity of Field — Refusal of 
Motor to Start — Slow Speed Without Load- — Idle Motors — Speed Regulation 
of Motor Without Load — Starting and Stopping Motors — Bad Contacts Be- 
tween Winding and Commutator Bars — Temperature of Commutator — 
Collector Rings — Materials of Commaitator — Loose Commutator Bars — 
Oval Commutator — A Gummy or Sticky Commutator Surface — Lubricat- 
ing the Commutator Surface — ^Erushes and Brush Holders — Brush Pres- 
sure—Replacing Brushes — Position of Brushes — Copper Brushes — Carbon 
Brushes — Setting Brushes — Hard Carbon Brushes — Lifting Brushes— End 
Motion in an Armature Shaft — Short Circuits in Armature — Sparking at 
the Commutator — Starting a Machine — Starting a Dynamo — Armature 
Running — Balancing of Armature — Centering of the Armature — Armature 
Out of Center — ^Foucault or Eddy Currents — Heating of Field Coils — 
Break in the Field Winding — Short Circuits in Field Winding — Earthing 
Dynarao Frames — Short Circuits in Outer Circuits — Wrong Connections in 
Compound Dynamos — Turning Down a Commutator — Sandpapering and 
Smoothing a Commutator — To Sandpaper a Commutator — Filing a Com- 
mutator — Short Circuits — Short Circuits Between Armature Windings and 
Frame — Alternator Brushes — Trouble in Rotors of Alternators — Self- 
Starting One-Phase Motor — Local Heating of the Windings of the Stator 
— Induction Motor Rotors — Svnchronous Motors — Polyphase Induction 
Motors — Field Ma.gnets of Alternators — Two-Phase Oper?tion — Break- 
downs in Transformers — Care of Transformers — Oil for Filling Trans- 
formers — Moisture in Transformers — Inspection of Transformers — Short 
Circuits in Transformers 416-438 

CHAPTER XXV. 

STATION NOTES. 

Temperature of Dynamo or Motor — Cleaning New Machine — Tnter- 
changeability of Parts — Cotton Waste — Access of Air — Oiling — Ring Oiling 
— Bearings — ^Safetv Fuses — Insulation of Windings — Broken Wires — Sol- 
dering — Nails, Tacks, and Iron Filings — Screws in Binding Posts — Cover- 
ing Machines — Emera-encies and Danscer Sisnals — Forgetfuiness and Neg- 
ligence — Keep One Hand in Your Pocket — Treatment of Electric Shock. 

439-444 

CHAPTER XXVI. 

SWITCHBOARDS. 

Switchboards — Panels — Air Switches — Oil Switches — Overload and 
Ur'derload Cut-Outs — ^Safety Fuses — Overload Circuit Breakers — Under- 



12 ELECTRICIANS' HANDY BOOK. 

load Circuit Breakers — MagTietic Release Underload Circuit Breaker — • 
Mechanical Release Underload Circuit Breaker — Reverse Current Circuit 
Breaker — Combined Circuit Breaker — Circuit Breakers as Switches — • 
Alternating-Current Potential Regulator — Direct Current Ground Indica- 
tor — Ground Alarm 445-457 

CHAPTER XXVII. 
VOLTMETERS AND AMMETERS. 

. The Voltmeter — Weston's Voltmeter — Damping Coil — Air Vane Damp- 
ing — Empire Voltmeters — Graduation of Voltmeter Scales — General ISotes 
on Voltmeters — Cardew Voltmeter — Hot Wire Instruments — The Stanley 
Hot-Wire Instrument — .Ammeters — Total-Current Solenoid Ammeter — ■ 
Shunted Ammeter — Transformer Ammeter — Wattmeter — Pressure Lines 
or Pilot Wires — Compensated Voltmeters— Compensators — The Ohmic 
Compensator — The Inductance Compensator 458-471 

CHAPTER XXVIII. 

DISTRIBUTION. 

Two Distribution Systems — Arc and Incandescent Lamp Circuits — Con- 
stant-Current Systems — Constant-Potential Systems — Series Distribution — 
Limitations — Features of Series or Constant-Current System for Arc 
Lamps — Calculations — Advantage of High Potential — Standard Series 
Lighting Current — Series Incandescent Lighting — Film Cut Out — Relief 
Lamps — Multiple Series System — "Municipal" Series Incandescent Light- 
ing — Series-Multiple System — Objections to Series Distribution — Parallel 
Distribution — Disadvantages of Parallel Distribution — Elementary Case 
of Parallel System — Potential Drop in Parallel System — Feeders, Mains 
and Leads — ^Classification — Loop System — Tree System — Closet System — 
Cylindrical and Conical Conductors — Calculation for Conical Conductor — 
Anti-Conical System — Anti-Parallel System — Individual Voltages of 
Lamps — Relations of Current to Drop — Uniform Potential Methods — 
Automatic Regulation of Voltage — -Independent Circuits — F'eeders — Auxil- 
iary Feeder Connections — Transfer Bus-Bar — Example — Feeder Economy 
— Three Wire System — Saving in Copper — Two-Dynamo Three-Wire Sys- 
tem — Single-Dynp.mo Three-Wire System — Three-Brush Dynamo — Storage 
Batteries in the Three-Wire System — Storage Battery Equalizer in Three- 
Wire System — Balancing Dynamo — Motor and Booster — Five and Seven- 
Wire System — High-Voltage Parallel Systems — Alternating-Current Dis- 
tribution — Individual Transformers- -Choke Coils — Y Connection for 
Alternating Current — Delta Connection — Joints in Line Wire — Insulators. 

472-512 

CHAPTER XXIX. 

ELECTRIC METERS. 

Electric Meters — Wattmeter — Edison's Meter- — Forbes' Meter — Thom- 
son's Meter — Shallenberger's Meter 513-517 

CHAPTER XXX. 

LIGHTNING ARRESTERS. 

Lightning Arresters — Lightning Protectors — Comb or Saw-Tooth. Ar- 
rester — Magnetic Blow-Out Arrester — Non-Arcing Metal Arrester — Dis- 
criminating Arrester — Westinghouse Lightning Arrester — Low Equivalent 
Alternating Current Lightning Arrester — Double-Pole Lightning Arrester 
■ — Tank Lightning Arrester c -- 518-522 



CONTENTS. 13 

CHAPTER XXXI. 
THE INCANDESCENT LAMP. 

Incandescent Lighting — The Incandescent Lamp — Tamidine Filaments 
- — Squirted Filaments — Carbonization — ^Calibration — Flashing — Occlusion 
of Gases by Filament — Lowering of Resistance by Flashing — Making 
Joints by Flashing — Pasted Joints — Electroplated and Other Joints — 
Leading-in Wires — Making the Lamps — Vacuum — Production of Vacuum 
— The Mercury Air Pump — Luminescence — Metallic Filaments — Oxide 
Filament — The' Nernst Lamp — The Glower — Glower Terminals — Heaters 
Ballast — The Cut Out — Direct Current Lamps — Vacuum Lamps — The 
Efficiency of the Nernst Lamp — Distribution of Light 523-534 



CHAPTER XXXII. 

THE ARC LAMP. 

The Voltaic Arc — Positive and Negative Carbons — Striking the Arc — 
Heat of the Arc— Voltage Drop — Counter Electromotive F'orce — The Re- 
sistance of the Arc Proper — 'Efficiency of the Arc Light — Quality of 
Carbons — Power Consamed in Arc — Effect of Air Blast — Effect of Magnet 
— Voltage Drop and Arc Length — Wearing of Carbons — Arc Light Car- 
bons — The Direct Current Open Arc — Distribution of Light in Direct- 
Current Open Arc — Commercial Rating of Arc Light — Hissing Arc — 
Light Given by Arc Proper — Resistance of Short Arcs— The Resistance of 
Longer Arcs — Stationary State — Alternating-Current Arc — Power Factor 
in Alternating Current Arc — Influence of Wave Form — Distribution of 
Light of Alternating Current Arc Lamps — Reactance Coil or Economy 
Coil — Efficiency of Alternatrng Current Arc Lamps — Noise — Duration of 
Carbons — Length of Arc — Id closed-Arc Lamps — The Action of the In- 
closed Arc — Globe and Carbon Holder — Inclosed Arc Lamp Carbons — 
The Clutch — Tripping Platform — Carbon Feed Lamps — Concentric Mag- 
nets — Dash Pots — Carbon Holders — Constant Current or Series Arc 
Lamp — Adjusting Weight — Action of an Arc Lamp on a Constant Po- 
tential Circuit — Action of the Resistance Coil in a Constant Potential 
Arc Lamp — The Parallel-Circuit System of Electric Supply — Constant- 
Potential Arc Lamps — Management of Inclosed-Arc Carbons — Adjusting 
Lamps — The Inclosing Globes — Negative and Positive Connections in 
Inclosed-Arc Lamps — Putting a Lamp Into Service — Oil — Clutcn Stop 
Adjustment — Cut-Out — Carbons for Inclosed Arc Lamp — To Carbon a 
Lamp — Lamps Without Mechanism — The Jablochkoff Candle — ^The Wal- 
lace Lamp — ^The Sun Lamp — Open-Air Incandescence 535-562 



CHAPTER XXXIII. 

PHOTOMETRY. 

Standards of Illuminating Power — Principle of the Photometer — Bar 
Photometer — Pnotometric Screens — The Bunsen Disk — The Leeson Disk — ■ 
Mounting the Disks — The Lummer-Brodhun Screen — The Standard English 
Candle — The Apparatus — Calculating the Scale of the Bar — The Observa- 
tion — Other Standards — Table of Photometric Standards — ^Shadow Photo- 
meter — ^Bouguer's Photometer— Foucault's Photometer — Direct Photo- 
metry of an Arc Lamp — The Luminometer — Pupillary Photometer — Dif- 
fractive Photometer — Spherical Candle Power — Candle Power of Incan- 
descent Lamps — The Photometry of the Arc Lamp — Mechanical Equiva- 
lent of Light — Watts per Candle Power in Arc Light — Watts per Candle 
Power in Incandescent Lamp — Quality of Arc Light — Distribution of 
Light from Arc Lamps in Service — Distribution of Light from Incandes- 
cent Lamps 563-588 



14 ELECTRICIANS' HANDY BOOK, 

CHAPTER XXXIV. 

ELECTRIC RAILROADS. 

The Electric-Car Motor — Standard Voltage and Allowable Temperature — 
Cause of Motor Heating — The Copper Loss — ^Determining the Heating of 
Motors — Conditions Causing Heating — Horse-Power of Car Motors — 
Traction Table — Construction of Electric-Car Motor — Switch Boxes and 
Circuit Breaker — Lightning Arresters — Controllers — Controller Points — ■ 
Driving Points: — Series-Parallel Controller — Hot Resistance — Blow-Out 
Magnet — Reverser — Board and Cut-Outs — Rheostat Controller — Motor- 
man's Duties — Economical Running — Excessive Use of the Brake — Flat 
Wheels — Sliding Wheels — Skidding Wheels — Reversing — Leaving the Car 
— Bad Ground — Refusing to Start — Fuses — Examining Connections — ■ 
Controller Troubles — Broken-Down' Controller — Motor Troubles — Emer- 
gency Stop — Jerking Car — Car Heating — Electric Radiators — Power Cir- 
cuit and Feeders — Insulators 584-608 

CHAPTER XXXV. 

ELECTRICAL MEASURING INSTRUMENTS. 

The Galvanometer — Simple Galvanometer- Astatic Galvanometer — 
Fiber Suspension — Reflecting Galvanometer — Arrangement of Reflecting 
Galvanometer — Translucent Scale — Plane Mirror Reflecting Galvanometer 
— The Thomson or Kelvin Galvanometers — Regulation of Sensibility — • 
The Ballistic Galvanometer — The Deprez-D'Arsonval Galvanometer — Bal- 
listic Measurement — Ballistic Calculation — The Tangent Galvanometer — 
The Sine Galvanometer — ^The Thomson or Kelvin Absolute Electrometer — 
Galvanometer Shunts — Compensating Resistance — Constant of a Galvano- 
meter — Determination of the Constant- — Figure of Merit — Galvanometer 
Resistance — Siemens's Dynamometer — Rheostats — Resistance Coils — Re- 
sistance Boxes — Resistance Wire — The British Association Standard Ohm 
— Arranp-ement of Coils — Siemens's Plan — Modern Arrangements — The 
Decade Plan — Details in Coxistruction of Resistance Boxes — ^Metal Spools 
— Practical Notes — Wheatstone Bridge or Bridge Box — Operation of the 
Wheatstone Bridge — -Null Methods — The Meter Bridge — Bridge Key — 
Shunt to the Galvanoscope — Proportional Coils — Galvanoscope — Condi- 
tions of Sensitiveness — Direction of Deflection — The Potentiometer — 
Principle of the Potentiometer — High-Voltage Determinations with the 
Potentiometer — Current Measurement with the Potentiometer. . .604-641 

CHAPTER XXXVI. 

ELECTRICAL ENGINEERING MEASUREMENTS. 

Voltmeter Measurement of Resistance — Voltmeter and Ammeter De- 
termination of Resistance — ^Low-Resistance Measurements — High Resist- 
ance Measurements — Line Insulation Tests — Rail-Joint Test — Measure- 
ment of Insulation Leakage — Insulation Resistance of a Metal Sheathed 
Cable — Determination of Capacity of a Cable — Galvanoscope Cable and 
Line Tests — Tpsts of Cable on Reels — Finding Wire Ends in a Cable — ■ 
Making Branch Connections in a Cable — The Telephone as a Galvano- 
scope — The Vibrating Magneto Bell as a Galvanometer — Varley Loop 
Test — Hand Magneto Tests — Hand Mag-neto Tests for Ground — Hand 
Magneto Test for Cross Connections' — ^Engineering Tests 642-658 

CHAPTER XXXVII. 

ELECTROPLATING. 

Electroplating — Energy Absorbed in Electroplating — General Principles 
^Anodes — Reproduction — Current for Electronlating — Regulation of Cur- 
rent— -Simple Plating Apparatus— Large Plating Apparatus— Metals De- 
posited—Copper Plating — Nickel Plating— Silver Platmg— Preparation 



CONTENTS. 15 

for Silvering — Gold Plating — Platinum Plating — Tin — Steeling — Size of 
Conductors — Current Intensity — The Relative Position of Anode and 

Surface to Be Plated — Temperature of Baths — Material of Vessels 

Metal Molds — Wax and Stearin Molds — Plaster Molds — Elastic Molds 

tiutta Percha Molds — Preparing Molds — Varnish — Oiling — Placing Molds 
in Lhe Bath — Plating on Molds — Backing Lp Deposits — Plating on Glass 
— Practical Processes iiod-^m 

CHAPTER XXXVIII. 

TELEPHONY. 

Sound — Pitch — Fundamental Note — Overtones — Sounding Plate — The 
Human Voice — Principle of Telephone Receiver — The Telephone Trans- 
mitter — Invention of the Microphone — Hughes Microphone — The Blake 
Transmitter — .Loose Carbon Transmitters — Hunning Transmitter — Edi- 
son's Telephone — The Solid-Back Transmitter — The Receiver — The Tele- 
phone Induction Coil — Dimensions of Telephone Induction Coils — Induc- 
tion Coils in Bracket Telephones — The Telephone Magneto — Polarized 
Bell — Telephone Systems — House Connections — Series Telephone Circuit — 
Bridged Telephone Circuit — The Hook-Switch — Common Battery Systems 
— Stone's Common Battery System — Dean's Common Battery System — 
Party Lines — Polarized Bells for Party Lines — Harmonic Signal for Party 
Lines — Distributing Boards — Repeating Coils — The Multiple Svs^itchboard 
— Operation of Switchboards — The Mechanical Annunciator — ^Lamp An- 
nunciator — Spring Jacks — Switchboard Connections — Lamp Signal Sys- 
tem — Conduction Interference — Induction Interference — Subscribers' 
Pole Connections — Improvements 677-717 

CHAPTER XXXIX. 

BELL WIRING. 

Bell Wiring — Size of Wire — Fishing — ^Work under Floors — Racing — ■ 
Leading the Wires — Grounding Wires— Soldering — Wires — Distinguishing 
Colors ; 718-722 

CHAPTER XL. 

ELECTRIC HEATING. 

Electric Cooking- and Domestic Heating — Power Required for Cooking- 
Efficiency — Electric Furnaces — Electric Arc Blowpipe — Eiectnc Soldering 
Iron — Electric Welding— Electric Incubator— Electric Radiator— Economy 
of Electric Heating 72d-7dO 

CHAPTER XLI. 

WIRELESS TELEGRAPHY. 

Wave Transmission of Signals — Hertz Receiver — Branly's Coherer — 
Wireless Telegraphv — Transmitting Apparatus — Receiving Apparatus — 
Connection of Stations — Antennre and Connections — Marconi s Coherer- 
Hysteresis and Other Receivers 7dl-7ob 

ERRATUM. 

Page 260, line 33 : For "Capacity" read "Inductance," 



Electricians' Handy Book. 



CHAPTER L 



MATHEMATICS. 



Electrical Calculations.— Electrical engineering involves m 
its practice much calculation. In the development of the theory 
of the science, the higher mathematics are employed; but m the 
more practical work of the science, and even in the study of its 
elementary theory, a slight knowledge of algebra and arithmetic 
is sufficient. Algebra is often regarded with dread, but if it is 
realized that algebra saves time and trouble and is easier than 
arithmetic in many cases, and that it provides a short road 
where arithmetic supplies a long one, it will be more favorably 
regarded. 

The object of such a book as the present is not to teach arith- 
metic or algebra. The reader will find some points noted under 
both heads which may be of interest. But in algebra the "four 
first rules," as they are called, addition, subtraction, multiplica- 
tion, and division, and the transformations -of simple equations, 
and' something of the theory of exponents, should be learned. 
Ohm's law is awkward for one to work with who is totally igno- 
rant of algebra. The simple rules for elementary calculations are 
expressed in algebra far more concisely than in words. Ratio and 
proportion, the old "rule of three," given in geometries as well 
as in algebras and arithmetics, is of value. 

Algebra.— The word "algebra" has a tendency to inspire the 
idea of difficulty and complication. This should not be so. 
Algebra is a system of short methods of attaining results, and 



18 ELECTRICIANS' HANDY BOOK. 

can be used extensively and to great advantage in electrical work 
by those who only know its four first rules, and the transforma- 
tions and solution of simple equations. 

The first law of electrical science that the student has to 
learn is Ohm's law. This law states that current strength is 
equal to electromotive force divided by resistance. This may be 
more concisely written thus: 

Electromotive force 

Current strength = 

Resistance 

Let a symbol be assigned to each of these quantities. Call 
current strength, I, electromotive force E, and resistance R; 
the law can then be written thus: 

_ ^ 

Three letters express a whole line or more of print. The last 
expression is an algebraic equation. It is evident that by using 
algebra to express a law much time and trouble may be saved. 

A quantity, such as 2 or 4, or it may be symbolized as A, 
can always be written as a fraction, without affecting its value. 
Thus these three quantities can be written: 

.. 2 4 A 

— — and — 
11 1 

The use of unity as the denominator does not change their 
value. If the transformations of algebra are applied to an 
equation expressing a law, the extent of the law will be more 
fully grasped than if a bare statement of it is taken. The divid- 
ing by unity is often useful. Ohm's law can be written thus: 

I E 

T "^ 

This equation can be read as a proportion or expression in the 
"rule of three," as it used to be called. It would read: 

I : 1 :: E : R 

This proportion states that if the current strength exceeds 
unity, the electromotive force must exceed the resistance, and the 
reverse. If the proportion is to be written out at full length it 



MATHEMATICS. 19 

would read: the current strength is to unity as the electromotive 
force is to the resistance. 

To keep this ratio true it is evident that if we multiply I by 
anything, we must multiply E by the same, or divide R by it. 
This is an algebraic discussion. Translated into words, it 
states that the current strength in a circuit can be increased by 
increasing the electromotive force in the same ratio or decreasing 
the resistance in inverse ratio. 

The equation is subject to algebraic transformations. If we 
preserve the unitary divisor, these changes can be pictured in 
the mind by imagining a diagonal cross to be placed between 
the two members of the equation; any quantity can be trans- 
ferred along the line pointing to it from one end to the other 
if the figure 1 is put in its place. Written out it should appear 
thus : 

r ^^^^ R 

R can join I as a multiplier; I can join R; or E can join 1. 
Any quantity deserting its place leaves unity behind it. This 
gives two good working forms of the equation, in the first of 
which the unitary divisor is omitted: 

I 1 

R I = E and — = — 
E R 

Algebra is the shorthand of arithmetic, and somie knowledge 
of it should be acquired. 

Direct and Inverse Proportion. — The expressions 
1 : 2 : : 5 : 10, 4 : 2 : : 1/3 : 1/6 
are complete proportions, and state that 1 is to 2 as 5 is to 10, and 
that 4 is to 2 as 1/3 is to 1/6. The first one states that 1 and 2 
are directly proportional to 5 and 10; the next one states that 4 
and 2 are inversely proportional to 3 and 6. 

An inverse proportion is written out exactly on the lines of a 
plain direct proportion, except that the reciprocals of one pair of 
quantities are used. A reciprocal is a fraction inverted, or for 
integral numbers may be described as unity divided by the 



20 ELECTRICIANS' HANDY BOOK. 

number. Either pair may be expressed fractionally in an inverse 
proportion. The two following are identical proportions: 

^ "^ • • 71 : 15, A : B : : JL . JL 



A • 13 U * 10 

Percentage. — If a percentage is expressed, it must be written 
as a whole number; thus, ten per cent is written 10%; fifteen 
per cent is written 15%. As these figures denote ten or fifteen 
for every hundred of the original quantity, they can only give 
a result as multipliers after division by 100. The division by 100 
is effected by putting in the decimal point; to divide a whole 
number by 100, the decimal point is placed so as to leave two 
digits to its right. It is immaterial whether the percentage 
figure, the original amount, or the result be thus divided. Thus, 
10 per cent of 175 may be calculated in three ways 

1.75 175 175 

10 0.10 10 

17.50 17.50 17.50 

The last is the simplest way; the second is the best way. An 
improvement in scientific nomenclature would be to abandon the 
term per cent, and to use decimals in its place, as ten one- 
hundredths or fifteen one-hundredths. Ten per cent would then 
be written, not thus: 10%; but thus: 0.1. 

This system lends itself to the reverse operation. Suppose it 
is asked what per cent of 175 26.25 is. We perform the division: 
26.25 -^ 175 = 0.15. Then multiplying 0.15 by 100 we get 15, which 
is our percentage, fifteen per cent, or 15%. It would be simpler 
to ask what decimal of 175 is 26.25. On dividing we would at 
once obtain the result without any multiplication by 100 or 
shifting of the decimal place. It would be 0.15, or fifteen one- 
hundredths. 

Fractions. — In expressing in speech or writing fractions having 
for denominator hundreds, thousands, or millions, some number, 
such as "one," should always be put before the denominator. 
Endless confusion results from neglect of this simple rule. Thus 



MATHEMATICS. 21 

"five hundred thousandths" might be interpreted to mean either 

500 5 



or 



1000 100,000 

The first should be expressed as five hundred one-thousandths, 
the second as five one-hundred-thousandths. Other numbers 
than one may apply. Thus we might have 
500 515 



or 



15000 1000 

which read five hundred fifteen-thousandths or five hundred and 
fifteen one-thousandths respectively. 

In naming fractions never use the word "over," as a over & tor 
a 

— . If it is a numerical fraction, say one-half or three-fourths, 
& 
or better yet, when applicable, "one divided by two," "three 

a 
divided by four." For literal fractions, such as — always say 

& 
a divided by &, and so for others. 

In addition to avoiding the inelegancy and incoherency of the 
"over" nomenclature, this fixes on the mind something that can- 
not be too firmly grasped; namely, that a fraction is a sign of 
division. % = 3 -^- 4. It may even be put as a process of long 
division, thus: 

4)3.00(0.75 
28 

20 

20 

Compound Fractions. — Compound fractions sometimes pre- 
sent a certain amount of difficulty. This is overcome completely 
if two things are kept in mind: First, that to divide one fraction 
by another, the divisor must be inverted and then the new nomi- 
nator multiplied by the nominator of the dividend, and the new 
denominator by the denominator of the dividend. Secondly, 
that any whole number can be expressed as a fraction by draw- 
ing a line under it and placing 1 beneath it. 



22 ELECTRICIANS' HANDY BOOK, 

Suppose % is to be divided by %. The latter is the divisor. 
It is inverted and the multiplication performed as described: 

_3_ 5 3 8 24 

Suppose % is to be divided by 5. We write 5 as a fraction, 

5 
namely, — , invert it, and multiply. 

3 5 3 13 



4*1 45 20 
The above operation can be expressed by a compound fraction. 
% divided by 5 may be written as a fraction, thus: 

_3^ 
4 
5 

which can be expressed by a division sign, thus: 

3^ ^ 5 =: 3/20 

The thick line in the compound fraction indicates that 5 is 
the divisor of the fraction. 

Let the same three numbers in the same order be written thus: 

3 

4 
5 

This indicates that 3 is to be divided by 4/5. We may express 
it thus: 

4 3 5 15 

The position of the thick line determines whether the result is 

3 15 

20^^T- 

The best plan in writing such fractions is to use an oblique 
line for the fractional component; thus, for the two examples 
given; 



J_ and 



4/5 



MATHEMATICS. 23 

It is to be regretted that this system is not more rigorously 
followed. 

The suggestion that such cases be dealt with by treating whole 
numbers as fractions with unity as denominator is applicable in 
many other cases. Many people advance in mathematics, and 
remain subject to a certain amount of confusion in just such 
points. An analogous and very common case is that of one who 
employs logarithms, but never uses the characteristic, relying on 
common sense for the decimal point, which is a very poor plan 
to follow. 

Inverted Addition and Subtraction. — When two numbers have 
to be added, the best way is to begin at the left hand. The same 
applies to subtraction. The process is termed inverted addition 
and subtraction. The following rules for these processes are 
abbreviated from Newcomb: 

Before adding two figures, notice if the sum of the preceding 
figures is greater than 9. If so, add 1 to the sum. If the sum 
of the preceding figures is exactly 9, then see if the next but one 
preceding figures exceed 9. If so, then 1 is to be added. If less 
than 9, add nothing. If equal to 9, try one more place to the 
right. 

Suppose we have to add the following: 

16786434 
53213566 



70000000 



Proceed as follows: Starting at the left, 5 + 1 = 6. The 
next figures to the right are equal to 9. Hence we must see if 
the next pair are greater than 9. They also are equal to 9. So 
we go on to the right until we find 4 + 6 = 10. Therefore we 
must add 1 to our first sum of the left-hand figures and put under 
them 7. The next two figures 6 + 3 = 9 have to have 1 added, 
and is written in all the way along until we get to 4 + 6 = 10, 
under which is written, giving us as sum the figures shown. 
It is very seldom that so complicated an example would occur. 



24 ELECTRICIANS' HANDY BOOK. 

Subtraction is performed on the same lines. An example fol- 
lows: 

37813241 
15294156 



22519085 

Proceed as follows: 3 — 1 = 2; 7 — 5 = 2; 8 — 2 = 6; but 
we see that 9 is greater than 1, the next couple to the right, so 
6 has to be reduced by 1, making 5 the next figure. 11 — 9 would 
be 2, but we see that 4 is greater than 3 in the next couple, and 
therefore write 1 in the next place, 13 — 4 gives 9, because 1 is 
less than 2 in the next couple. 2 — 1 would give 1, except that 
5 is greater than 4 in the next couple. Therefore is written. 
14 — 5 gives 8, because 6 is less than 1 in the right-hand couple, 

ilultiplication and Division. — In many cases a multiplier or a 
divisor can be factored or divided into two single digits, which 
multiplied together will produce the number. Thus, if we have 
as multiplier 63, it can be expressed as 9 X 7. To multiply a 
number by 63, we may first multiply by 9, and then multiply the 
product by 7, or the reverse. 

Suppose we have a lot of wires of 749 circular mils each; and 
suppose that 49 of them are to be put in parallel. What is the 
sum of their areas? We may say 749 X 49 = 36,701; or as 
49 = 7 X 7, we may say 749 X 7 = 5243; and 5243 X 7 = 
36,701. 

The answer by either method is 36,701 circular mils. 

Suppose that 27 feet of wire is found to have a resistance of 
22.3 ohms. What is the resistance of a foot of this wire? It 
may be calculated by long division: 22.3 h- 27 = 0.8259; or as 
27 = 3 X 9, we may say 22.3 -^ 3 X 7.4333, and 7.4333 -^ 9 = 
0.8259. 

The answer by either method is 0.8259 ohm resistance per 
foot. 

The latter example could have been done by dividing in suc- 
cession three times by the number 3, thus: 22.3 -^ 3 =: 7.4333; 
7.433 -^ 3 = 2.4777; 2.4777 -^ 3 — 0.8259. 

Certain products may be memorized. Thus 256 is the product 
of 16 by 16 or of 8 by 32; 125 is the product of 5 by 25; 625 is 



MATHEMATICS 25 

the product of 25 by 25, One who is much engaged in arithmet- 
ical computations acquires a stoclv of these products. 

To multiply by 5 annex one cipher to the number and divide 
by 2. Thus, 78 X 5 = 780 4- 2 = 390. 

To multiply by 25 .annex two ciphers and divide by 4, Thus, 
69 X 25 = 6900 -^ i = 1725. 

To multiply by 15 annex a cipher to the quantity and add 
thereto one-halt of the new quantity. Thus, 181 X 15 = 1810 + 
905 = 2715. 

To multiply by 125 annex two ciphers to the quantity and add 
thereto one-quarter of the new quantity. Thus 181 X 125 = 
18,100 -f 4525 = 22,625. 

Anyone can extend the general process here indicated indefi- 
nitely. 

To multiply the squares of several numbers, multiply the 
original numbers and square the product. Thus, 81 X 64 X 49 
1= (9 X 8 X 7)- = 504- = 254,016. 

If the two last digits of a number are divisible by 4, the whole 
number is divisible by 4. Thus 1924 is divisible by 4, because 
24 is; but 1914 is not divisible by 4, because 14 is not. 

If a multiplier lies between 1 and 200, the multiplication by 
it can be effected by percentage addition, or subtraction. Thus 
to multiply by 101 add one per cent to the number and multiply 
by 100. The multiplication is done by moving the decimal point 
two figures to the right, or what is the same, by carrying out 
the number two places in that direction by adding two ciphers. 
Suppose 2029 X 101 is required. One per cent of 2029 is 20.29. 
Adding this to the original number, we have 2029 -+- 20.29 = 
2049.29. Moving the decimal point two figures to the right, we 
have 204,929. 

The rule is to take the difference between the multiplier and 
100 as a percentage. Multiply by 100 and add or subtract as the 
multiplier is larger or smaller than 100. 

Thus, to multiply 2029 by 75, first multiply by 100. This gives 
202,900. The difference between 75 and 100 is 25. As 75 is less 
than 100, 25 per cent of 202,900 is to be subtracted from it. 
202,900 — 50,725 = 152,175. 

To divide accurately by the percentage method, the divisor 



26 ELECTRICIANS' HANDY BOOK. 

must be taken as the basis of the percentage. The number is 
first divided by 100 by moving the decimal point two figures to 
the left. Then to or from the result is added or subtracted the 
percentage of the divisor which the di-fference between it and 
100 is. Thus, for the divisor 75, the difference between it and 
100 is 33 1/3 per cent of 75. 

To divide approximately by such numbers, the regular way is 
generally the best, except for numbers near 100. Then per- 
centages can be added or subtracted for an approximate result. 
Thus, to divide by 95, add 5 per cent; to divide by 105, subtract 
5 per cent, in both cases dividing by 100. This is only approxi- 
mate. To divide by 105 we should by the percentage method 
subtract 4.762 per cent and not 5 per cent, and multiply by 
100. To divide by 95 we should add 5.263 per cent and not 5 
per cent, and multiply by 100. 

The percentage method is more easily applied to multiplication 
than to division. 

Two numbers of two places each, and which have the same 
figure in the unit places or in the ten places can be multiplied 
together thus: Multiply unit by unit. If the figures in the 
ten places are alike, add the unit figures together and multiply 
by the quantity in the tens of one number. Then mfultiply the 
tens. Add the three for the answer. Thus, to multiply 47 by 49: 

9X7= 63 

9 -f 7 = 16; 16 X 40= 640 

40 X 40 = 1600 

2303 

If the figures in the unit places are the same, multiply the 
units as before; add the quantities in the tens of both numbers, 
and multiply by the units in one number. Multiply the tens, 
and add the three products. Thus, to multiply 74 by 94: 

4X4= 16 

90 -1- 70 = 160; 160 X 4= 640 

90 X 70 = 6300 

6956 



MATHEMATICS. 27 

Two numbers ending in 5 can be multiplied by a similar pro- 
cess. Multiply together the figures to the left of the 5 in one 
number by the corresponding figures in the other number. Add 
to the product one-half the sum of the numbers just multiplied to- 
gether and annex 25. 

Thus to multiply 65 by 75: 

1^ 

7 + 6 = 13; _ = 6.5 

2 
7X6 = 



4875 

The decimal place is used above in order to indicate where the 
25 is to be annexed; it goes next to the decimal place if such is 
required. If the sum of the tens is an even number, no decimal 
place appears. 

Squares of Numbers. — If we know the square of any number, 
we can obtain the square of the number next above it by adding 
to the known square the sum of the numbers. 

Thus, 12- = 144. This is a familiar number. To obtain from 
it the square of 13 we simply add 12 + 13 = 25 to it, giving 169, 
which is the square of 13. Suppose we know that 16^ = 256; 
then by adding 16 + 17 to it we get 256 + 16 + 17 = 289 = 17^ 

The converse is true. We may by subtracting the original 
number and the one below it get the square of one next lower 
than the first one. Thus, 16^ = 256; 256 — (16 + 15) = 225 
= 15^ 

There is a certain value in this for the calculation of the 
squares of odd numbers. The squares of even numbers can be 
calculated by an easy method if they can be factored or divided 
into two factors, one less than 12 and the other less than 3. 
When thus divided, square both factors and multiply the squares 
together. The reason for restricting the process to numbers 
with small factors is to have the small square less than 16. 
Anyone can multiply by 9 mentally; but it is not so easy to 
multiply by 16. 



28 ELECTRICIANS' HANDY BOOK. 

Suppose' 18 is to be squared. This can be factored as 6 X 3. 
Squaring both and multiplying, we have 36 X 9 = 324. Or it 
may be factored as 9 X 2. Proceeding as before, 81 X 4 = 324; 
18=^ = 324. 

This is only applicable to even numbers. The passage to the 
square of an odd number is done by the method just described. 
Suppose 19 is to be squared. By the above method we find that 
18- = 324; adding to 324 the sum 18 + 19 = 37, we have 361 1= 19-. 

The largest number to which it is worth while to appl^'' these 
combined processes is 36, which factors into 12 X 3. Squaring, 
we have 144 X 9 = 1296 r= 36-. 

A very easy way of squaring numbers less than 100 is the 
following: Subtract from the number to be squared the differ- 
ence between it and the next multiple of 10 just above it. 
Multiply the reduced number by the multiple of 10 and add the 
square of the difference between the original number and the 
multiple of 10. 

Suppose 37 is to be squared. 40 is the next multiple of 10, and 
3 is the difference. 37 — 3 = 34; 34X40 = 1360; 3- = 9; and 
1360 + 9 = 1369. 

The multiple of 10 next below may be used if nearer the 
original number. The difference is to be added to the original 
number, the multiplication is effected, and the square of the 
difference is added. 

Suppose 63 is to be squared. 60 is the nearest multiple of 10, 
and 3 is the difference. 63 + 3 = 66; 66X60 = 3960; 3- = 9; 
and 3960 + 9 = 3969. 

The proof is demonstrated by algebra. Let a be the number to 
be squared, and 1) be the decimal next above it; let 6 — a:=m. 
Then & = a + m, and the reduced number ^=a — m. By the rule 
(a + m) X {a — m)=.a- — &^ or the product is equal to a- less 
h'-, and to get a-, 1)- must be added to the product. But by the 
regular formula the product of the sum and the difference of two 
numbers is equal to the difference of their squares. 

A number ending in 5 can be squared or multiplied by itself 
thus: Multiply the figures next to the 5 on its left by a num- 
ber one higher, and annex 25 to the product. Thus to square 
25 we proceed as follows: 2 is the figure next to 5 on its left; 



MATHEMATICS. 



29 



3 is the number one higher than 2. 2X3 = 6. Annexing (not 
adding) 25, we have as the answer 625. To square 165 we mul- 
tiply 16 by 17, giving 272, and annexing 25 we have 27,225 as 
the answer. 

Cancelation. — Cancelation is a process which is rather neg- 
lected, yet which may be very useful. 

Suppose we have to divide 1894 by 707. Instead of doing it 
by long division, we may apply cancelation, thus: 

101 I 270.571 

We have divided both numbers by 7, and canceled the original 
ones. Instead of dividing by 101, we simply diminish 270.571 
by 1 per cent, which is done by subtracting from it 1/100 of 
itself, thus: 270.571 — 2.705 = 267.865, for an app-roximate result. 

It is obvious that cancelation is not always of much use. In 
the above example it is only of value as it enables us to use the 
percentage method. Often numbers are so intractable that can- 
celation is quite inapplicable. The essential is that the divisor 
shall be divisible by some number without giving a remainder. 
Cancelation always gives a simplification in such cases, but it is 
often hardly worth while to use it. 

The limitations of the percentage method must be kept in 
mind. Often as above the only thing«which makes cancelation of 
value is the applicability of the percentage method. 

Power of Ten or Exponential Notation. — This adjunct to 
calculations has become almost indispensable in working with 
units based on the C. G. S. system. It consists in using some 
power of ten as a multiple, which may be called the factor. The 
number multiplied may be called the characteristic. The fol- 
lowing are the general principles. 

The power of 10 is shown by an exponent which indicates the 
number of ciphers in the multiplier. Thus 10- indicates 100; 10^ 
indicates 1,000 and so on. 

The exponent, if positive, denotes an integral number, as 
shown in the preceding paragraph. The exponent, if negative, 
denotes the reciprocal of the indicated power of 10. Thus IO-2 

1 1 

indicates ; IQ-s indicates and so on. 

100 1000 



30 ELECTRICIANS' HANDY BOOK. 

The compound numbers based on these are reduced by multi- 
plication or division to simple expressions. Thus: 3.14 X 10^ = 

3.14 

3.14 X 10,000,000 = 31,400,000. 3.14 X 10-^ = ^ or 

10000000 

Regard must be paid to the decimal point as is done 



IOjUUUUuUU 

here. 

To add two or more expressions in this notation if the ex- 
ponents of the factors are alike in all respects, add the character- 
istics and preserve the same factor. Thus: 

(51 X 10«) + (54 X 10«) =: 105 X 10^ 
(9.1 X 10-^) + (8.7 X 10-9) = 17.8 X IQ-^. 

To subtract one such expression from another, subtract the 
characteristics and preserve the same factor. Thus: 
(54 X 10«) — (51 X 10*^) =3 X 10*^. 

If the factors have different exponents of the same sign the 
factor or factors of larger exponent must be reduced to the 
smaller exponent, by factoring. The characteristic of the expres- 
sion thus treated is multiplied by the odd factor. This gives a 
new expression whose characteristic is added to the other, and 
the fkctor of smaller exponent is preserved for both. 

Thus: 

(5 X 10^) + (5 X 10«) = (5 X lOO + (5 X 100 X 10^) = 505 X 
10^ 

The same applies to subtraction. Thus: 

(5 X lO'') — (5 X 10^) = (5 X 100 X 10^) — (5 X lOO = 495 X 

If the factors differ in sign, it is generally best to leave the 
addition or subtraction to be simply expressed. However, by fol- 
lowing the above rule, it can be done. Thus: 

Add 5 X 10-2 and 5 ^ ^q3^ 

5 X 103 = 5 X 10^ X i;^-2 . (5 v< 10^ y^ 10-2) + (5 X 10-^) = 

500005 
500005 X 10-2. This may be reduced to a fraction ■ — = 

100 

5000.05. 

To multiply add the exponents of the factors for a new factor, 
and multiply the characteristics for a new characteristic. The 



MATHEMATICS. 31 

exponents must be added algebraically: that is, if of different 
signs the numerically smaller one is subtracted from the other 
one, and the latter's sign is given the new exponent. 

Thus: 

(25 X 10«) X (9 X 10^) = 225 X 10^*. 
(29 X 10-^) X (11 X 10") =319 X 10-^. 
(9 X 10*) X (98 X 10^) = 882 X 10^°. 

To divide, subtract algebraically the exponent of the divisor 
from that of the dividend for the exponent of the new factor, and 
divide the characteristics one by the other for the new character- 
istic. Algebraic subtraction is effected by changing the sign of 
the subtrahend, subtracting the numerically smaller number from 
the larger, and giving the result the sign of the larger num- 
ber. (Thus to subtract 7 from 5 proceed thus: 5 — 7= — 2.) 

Thus: 

(25 X 10«) -^ (5 X 10*^) =5 X 10-2 
(28 X 10-«) ^ (5 X 10^) =5.6 X 10-" 

Logarithms. — The use of logarithms can be learned in a few 
hours. All manuals of algebra give the theory, and the applica- 
tion with examples is generally given in manuals of trigonometry. 
The table of logarithms is generally given in the latter manuals, 
but not in algebras. 

Logarithms should be taken in the right aspect, as an aid to 
multiplication and division and extraction of the square root, and 
as an almost indispensable assistance in extracting higher roots. 
They assist immensely in arithmetic, and thorough familiarity 
with them should be acquired. 

The only point which presents the least difficulty is the charac- 
teristic — for some obscure reason this is regarded as a sort of 
obstacle by the beginner. There is even a tendency to omit it 
altogether in calculations. This tendency is a very bad one. 
The characteristic should be written out always, because sooner 
or later cases will arise when its absence will occasion confusion 
and error. 

The logarithms of constants are often included in tables of 
logarithms, and are frequently very useful. 

A number of tables of logarithms are published in book form. 
In purchasing one. see that the type and printing are clear. 



32 ELECTRICIANS' HANDY BOOK. 

Angular ileasurement. — A unit circle is a circle whose radius 
is equal to 1, or whose diameter is equal to 2. 

Angles are measured by the fractional part of the arc of a 
circle which they include in their sweep. The arc of an entire 
circle is divided into 360 parts called degrees, and indicated by a 
little circle at the top of and following the figures, thus: 45°, 90°, 
reading "45 degrees," "90 degrees." It will be observed that the 
angle has no linear measurement, feet or inches for example. 
The degrees assigned to it express its proportional measure- 
ment, the whole circle being taken as equal to 360°. 

45 97 ^ 

Thus 45° are -i— or % of an entire circle, 27° are * . or -2. 
360 360 4u 

of an entire circle. 

The length of the circumference of a circle is expressed in 
terms of its diameter, thus: 7t d, d standing for diameter, and 
7t for 3.14159 + . 

In alternating current formulas, some quantities are used 
which are what are known as functions of angles. Such are the 
sine, cosine and tangent. These three are the principal ones 
employed in alternating current formulas, and are all that will be 
described here. 

The cut, Fig. 1, shows a circle. It has two lines drawn across 
it through the center. Such lines are called diameters. One- 
half of a diameter measured from the center to the circumfer- 
ence is called the radius. The angles begin at the right-hand end 
of the horizontal diameter, and are counted toward the top of 
the circle, and so all around it against the movement of the 
hands of a clock. The upper end of the vertical diameter marks 
the end of an angle of 90°; the left-hand end of the horizontal 
diameter, an angle of 180°; the lower end of the vertical diame- 
ter, an angle of 270°; and coming back to the starting point, the 
right-hand end of the horizontal diameter, an angle of 360°, or 
one of 0°, according to how it is taken. 

Radian System ~of Angular ileasurement. — A radian is the 
angle measured by the arc of a circle equal in length to the radius. 
The circumference of a circle of radius 1, which is the unit 
circle, is 2 5r, which is equal to 6.2832 — . A circle with a radius 
of 10 inches measures about 62.8 inches around. The circumfer- 



MATHEMATICS. 



iZ 



ence of a circle contains 2 7t radians; a radian is equal to one 
circumference of a unit circle divided by 2 tt . Radians are 
shown in Fig. 2; they are the six equal angles which nearly fill 
the circumference. 

As the circumference of a circle is equal to 360 degrees, a 

360° 

radian is equal to 360° -^ 2 7t, or = 57.3° approximately. 

6.2832— 

When 2 7t appears in a formula, it is generally in the radian 
system. 





Fig. 1.— Sine, Cosine and Tangent. 



Fig. 2.— Radians. 



Trigonometric Functions. — Fig. 1 is a circle. It is divided 
into quarters by two diameters, one horizontal and one vertical. 
The quarters are designated by numbers, and referred to their 
arcs, which are quadrants. The upper right-hand quadrant is the 
first quadrant; the upper left-hand quadrant is the second quad- 
rant; and the lower left-hand quadrant is the third quadrant, and 
the other is the fourth quadrant. 

A radius OA prolonged outward determines an angle in the 
first quadrant. The vertical line from the outer end of the 
radius to the horizontal diameter is the sine of the angle. This 
sine is marked AB; the angle is included between the lines OD 
and OA. 



34 ELECTRICIANS' HANDY BOOK. 

The sine of an angle is always a vertical line, and is always 
measured up or down, as the case may be. 

The horizontal line from the outer end of the radius A to the 
vertical diameter is the cosine of the angle. The line BA is the 
cosine of the angle. 

The tangent of an angle is the vertical line from an extremity 
of the diameter to the prolongation of the radius marking the 
angle. For the angle shown, the tangent is the line indicated by 
the letters D C. 

The numerical value of the sine divided by that of the cosine 
gives the numerical value of the tangent. 

Numerical Values of Circular Functions are expressed in 
terms of the radius, whicn is taken as 1 except in logarithmic 
tables, when it is taken as lO'''. The value when logarithms are 
dropped is taken again as 1. The value can be applied to a circle 
of any radius by multiplying it by the radius of the circle in 
question. 

Greek Letters.— jr. This is the Greek letter p. It is best 
pronounced "pi" If the Continental pronunciation "pee" is used, 
there is danger of confusing it with the English letter p. Sup- 
pose that a quantity denoted by p is to be multiplied by 7t ; con- 
fusion would at once ensue if 7t was called "pee" and not "pi." 
It indicates the factor by which the diameter of a circle must be 
multiplied to give the circumference. For approximate calcula- 
tions its value may be taken as 3 1/7, or what is the same thing, 
22/7. If decimals are to be used, 3.1416 or 3.14159 may be used, 
the latter being accurate enough for almost any purpose. The 
very usual custom of multiplying the diameter by 3 to get the 
circumference is so very inaccurate that it should never be used. 

Take a circle of 37 inches diameter. Multiplied by 3 it gives 111 
inches circumference. Multiplied by 3 1/7 it gives 116 2/7 or 
116.286 inches circumference. Multiplied by 3.1416 it gives 116.239 
inches circumference. Multiplied by 3.14159 it gives 116.2388 
inches circumference. 

Reduced *to sevenths, the last two products read between 
1/7 and 2/7 for their fractional part. The error in 116 2/7 is 
only 0.0469 inch, or about 1/20 of an inch. It is evidently un- 
necessary tor every-day work to use the decimal expressions. 



MATHEMATICS. 35 

The exact value of tt has never been calculated. It has been 
deduced to over a hundred places of decimals. 

e. This is the Greek "th," or theta, a double letter as we 
would call it in English; it is really an aspirated "f." It is used 
a great deal in alternating current calculations, to indicate the 
angle of lag in alternating current work. 

ip. This is the Greek "ph," or phi, an aspirated p; it is 
used to indicate the angle through which an alternating current 
wave has advanced from the 0° position. When vector diagrams 
are used, the measurement begins from the right-hand end of 
the horizontal diameter. 

CD. This is the Greek o (long). It is spelled omega and pro- 
nounced as spelled. It is used to indicate the frequency of an 
alternating current in radians per second. Let f equal the fre- 
quency per second of the alternations of a current; then ca = 
2 7f f. A single cycle takes 2 ;r or 6.2832 radians for its comple- 
tion. If the numerical value of co in any given case is divided 
by 6.2832, the quotient will be the number of cycles per second. 
The product of oo by t, or co t, is equivalent to qj in formulas re- 
lating to alternating current. 

Useful Constants. — There are certain constants and figures of 
frequent use which should be memorized. The value of 7t is one 
of these. It is approximately 3 1/7, 3/22, or 3.14159. 

The radius of a circle squared is equal to one-fourth of the 
square of the diameter. One-fourth of 7t is 0.7854. This is a 
good figure to remember. The area of a circle is equal to the 
square of its radius multiplied by tt (3.14159), or to the square of 
its diameter multiplied by ;zr/4 (0.7854). Thus a circle of one 
foot diameter is 0.7854 square foot area; one of two feet diameter 
is of one foot radius and of 3.14159 square feet area. 

The factor 0.7854 shows that a circle is approximately 8/10 
the area of the square inclosing it. This gives a quick method 
of approximately finding the volumes of round cisterns and 
tanks. Suppose a round tank is 12 feet in diameter and 15 feet 
deep. The area of the inclosing square is 12X12=: 144 square 
feet. 144 X 8/10 = 115.2 the approximate area of the round cis- 
tern, and 115.2 X 15 = 1728 cubic feet. This is the approximate 
volume, which can be made quite close to the truth by the per- 



36 ELECTRICIANS' HANDY BOOK. 

centage method. It is evident on inspection that 0.8 exceeds 
0.7854 by a little less than 2%. 1728 less 2% is 1728 — 34 = 1694. 
The correct answer is a little over 1696. 

Many other practical factors and quantities may be noted. 

A speed of one mile an hour is equal to 1.45+ foot or 1 foot 
5%+ inches per second. 

A railway train going one car length per second goes at about 
40 miles an hour. 

One hundred yards in 10 seconds is about 20 miles an hour. 

The number of 30 foot rails passed over in 20 seconds is the 
approximate speed in miles per hour. 

The pull on the draw bar of a car on a level is about 20 
pounds per ton per mile an hour. Thus at two miles an hour it is 
40 pounds per ton, and so on. 

A cubic inch of water makes nearly a cubic foot of steam at 
atmospheric pressure, half this volume at 15 pounds pressure, 
one-third at 30 pounds pressure, and so on. 

Water is 816 times heavier than air. 

A cubic inch of iron weighs nearly one-quarter of a pound; 
a cubic inch of copper, 0.32 pound; of lead, 0.41 pound. 

A cubic foot of water weighs about 62i^ pounds. 

To reduce kilometers to miles, multiply by 0.6 and add one-thir- 
tieth. 

Sixty-two miles an hour is 100 kilometers an hour. 

1 kilowatt is equal to a little over 11/3 horse-power (1.3404). 

1 B.T.U. (British thermal unit) is equal to 772 foot-pounds. 

1 cubic foot of air weighs 537 grains. 

1 cubic foot of hydrogen weighs 37 grains. 

1 liter of hydrogen (the crith) weighs 0.08961 gramme. 

Torque. — Torque is force exercised in the rotation of a wheel 
or similar object, or the force which a rotating wheel or similar 
object exerts. Thus, in the case of an electric motor its twisting 
force, or the force with which its shaft is rotated, is its torque. 
The armature of an active dynamo resists the force which the 
belt exercises on the belt wheel, and energy or horse-power has 
to be used to keep it going. This resistance is torque. The 
strain produced by the belt is driving torque; the resistance 
offered by the belt-wheel keyed on the armature shaft is the 



MATHEMATICS. 37 

resisting torque, strictly speaking. Of these two terms, the one 
most used is driving torque only. In a motor the case is re- 
versed. The armature is drawn around and kept in rotation hy 
the field magnets, and the armature exercises torque, and by 
means of its torque, and because of it, can drive machinery. In 
the generator, the belt exercises torque; in the motor, the arma- 
ture exercises it. 

If we know the torque and the speed of the machine, we have 
the actual horse-power. 

Torque is usually expressed in this country in pounds pull 
on a one-foot radius, which is that of a 2 foot pulley or belt- 
wheel. 

The horse-power exerted by a motor whose speed and torque 
are known may be calculated by the following formula. In it T 
indicates torque, H. P. horse-power, r radius of torque, S revo- 
lutions per minute of the motor shaft. 

T X r X 6.28 X S 

H. P. = 

33,000 

Suppose the torque exerted by a 4-foot belt-wheel driven by a 
motor was 10 pounds, and that the motor made 2,000 revolutions 
per minute. Substituting these figures, the formula becom,es: 

10 X 2 X 6.28 X 2000 r51,200 

H. P. = — ^ = 7.612 

33,000 ~ 33,000 

actual horse-power. 

If a machine is rated at a definite horse-power and speed, the 

torque is calculated by the next formula, which is a transposition 

of the other. 

H. P. X 33,000 

T= 

r X 6.28 X S 

Suppose a 7% horse-power machine has a speed of 2,000 revolu- 
tions at full load. To determine the torque on a pulley of 4 feet 
diameter, which gives r=2, we substitute as below: 

7% X 33,000 255,750 

T = ^^ _ . ^ ^^ = 10.18 pounds torque at 2 feet 

2 X 6.28 X 2000 25.120 

radius. 



38 



ELECTRICIANS' HANDY BOOK. 



In these formulas the factor 6.28 is 2 tt , or the factor by which 
the radius of a circle must be multiplied to give the circumfer- 
ence. 

It is practically accurate to consider the torque of an electric 
machine identical when run either as dynamo or motor if the 
speed and current are the same. In many cases it is easy to run 
a dynamo as a motor. The Prony brake in some of its many 
forms can be applied, and the torque determined with the simplest 
possible appliances. The torque developed by the dynamo when 
run as a motor is taken as that which would be absorbed by it 
when run as a dynamo. 

Actual horse-power, or that exerted by a machine, is often 




S'la. 3.— PaoNY Brake. 



called brake horse-power, because it is determined by a Prony 
brake. 

The Prony Brake is an apparatus for determining the horse- 
power of a machine, such as a steam engine, or electric motor, or 
dynamo. A Prony brake is shown in Fig. 3. A belt pulley is 
turned by the machine under trial; the pulley is keyed to the 
sliaft M. A strap brake passes around it, armed with wooden 
shoes. One end of the strap is fastened at D, the other at B'. 
The latter fastening is adjustable by the screw and hand-wheel 
S. The arrow indicates the direction of rotation of the wheel. 
The hand-wheel S is turned until the weight is just held in equi- 
poise, with the lever between the two stops. A spring balance 
is often used instead of the weight. The shaft under the con- 
ditions outlined above rotates with power enough to sustain the 
weight on the lever or that indicated by the spring balance. 
Calling tlitj half diameter or radius of the pulley r, and the dis- 



MATHEMATICS. 39 

tance from the center of the shaft to the point of application 
of the weight L, we have for the turning stress or force, which 
is torque, of the shaft M: 

Pull X r 
Torque = 

From the torque thus determined and the number of revolu^ 
tions the horse-power is obtained by the formula below: 

6.28 S 

Horse-power ==: Torque X ■ 

33,000 

in which S is the number of revolutions per minute made by the 
machine. The torque is the force component, the rotation of 
the shaft is the space component, and the two give energy, and 
the energy rate is power. 

The Dynamometer is an appliance which indicates the power 
a machine at work in exerting, when the speed of the machine 
is known, indicating directly the force. This force may be exer- 
cised directly, as when a team of horses is pulling a wagon or 
when a locomotive engine is pulling a train of cars. A spring 
balance used as draw bar or coupling link is a dynamometer for 
such cases. Its reading in pounds multiplied by the speed of 
the horses or engine in feet per minute, and divided by 33,000, 
gives the horse-power. 

If the dynamometer gives the torque or pull of a belt, then the 
radius of the pulley must be known, and the revolutions per min- 
ute. Formulas will then give the horse-power. 

In the illustration. Fig. 4, a- transmission dynamometer is 
shown. It transmits the power of a machine, whence it derives 
its title, c is a shaft connected by a universal joint c' to the 
machinery to be driven. The pulley C with inside teeth is keyed 
to this shaft. It is turned by the pulley B, and B is turned by 
the pulley A, to whose shaft a a with universal joint the working 
machine is connected. Noting the directions of rotation indi- 
cated by the arrows, it will be seen that B driven by A has its 
axle forced downward. It is acted on with more or less force, ac- 
cording to the power exercised by the machine. The lever D, on 
which B is mounted, has a limited range of motion about its ful- 



40 



ELECTRICIANS' HANDY BOOK. 



crum at D. This motion is counteracted by the weight P, acting 
through the lever T on the knife edge e of the lever D. The 
torque can be taken at any time without interfering with the 
running of the machine, and without absorbing any of its power. 
Luminiferous Ether. — ^^This is a theoretical thing whose exist- 
ence has never been proved. It is assumed to be the cause of the 
dissemination of light and of the phenomena of electricity. It is 

best thought of as something like 
a gas but so much more tenuous 
that it cannot be detected in any 
way. It passes through many 
substances, especially through 
non-conductors of electricity 
such as glass. Conductors of 
electricity are almost impene- 
trable by it. On this distinc- 
tion between transparent and 
opaque bodies, the first not con- 
ducting electricity and the others 
conducting it, is found a basis for 
the theory that light and elec- 
tricity are closely related. Clerk 
Maxwell's celebrated electro- 
magnetic theory of light leads 
to the same conclusion, and a 
confirmation for it may be 
found in the opacity of conduc- 
tors such as metals and gra- 
phitic carbon and the transpar- 
ency of non-conductors such as 
glass, amber and carbon in the 
modification known as diamond. This is a general statement, 
and open to qualifications which it is unnecessary to introduce 
here. 




€ 


ib 


1 


1 


|- 1 


<iiiii 




Mil slllllli 




11 


1 


i 


iMf. 






i-M 




^ 


' — «"-T"^ 







Fig. 4.— The Dynamometeb. 



CHAPTER II. 

ELECTRIC QUANTITY AND CURRENT. 

Electric Quantity. — While electricity is about the most in- 
definable word used in science, we have as a starting point to 
assume that it is of such a nature as to be susceptible of possess- 
ing quantity. We have to use the conception of definite and 
definable quantities of electricity without being able to say what 
we mean by electricity itself. The conception of an electric cur- 
rent is that of the transfer of quantities of electricity along a 
wire or conductor, just as in a current of water gallons are 
transferred through a pipe. An electric current heating the 
filaments of incandescent lamps, producing the electric arc be- 
tween carbon terminals, exciting electric magnets and driving 
powerful motors, is familiar enough. But the idea of quantities, 
stored up in receptacles, is less so. 

A quantity of electricity may be stored upon the surface of 
any insulated body. Coincident with its storage is the storage 
of another equal quantity of opposite polarity somewhere else. 
A quantity of electricity cannot be stored or charged upon a 
surface unless an equal and opposite charge is stored elsewhere. 

It is something like chemical decomposition. It is impossible 
to take a quantity of hydrogen from water without producing a 
corresponding quantity of oxygen, equal thereto in saturating 
power. 

Storage of Electric Quantity. — The surface of bodies seems 
to be the only part concerned in the storage of electricity. The 
coexistence of two charges and the impossibility of a single 
charge existing by itself, caused the early investigators to found 
the two-fluid theory of electricity. Current phenomena are 
treated more simply by assuming the existence of a single elec- 
tric fluid. The assumption is therefore made, although rather 
out of harmony with the Phenomena of electric charges. 



42 ELECTRICIANS' HANDY BOOK. 

One of these phenomena is that two oppositely-charged surfaces 
attract each other, and that their charges tend to combine, form- 
ing a current while doing so. But the single-fluid versus double- 
fluid controversy is an academic question; there is certainly no 
fluid in electricity; and we can speak of a current as of water, 
or of positive and negative charges as of oxygen and hydrogen 
in the water molecule ad libitum. 

Condensers. — The typical receptacle for electricity is termed a 
condenser. It comprises two surfaces adapted to receive and to- 
conduct electricity, insulated from each other. To enable the 
surfaces to conduct electricity to every part of their area, and to 
give it up when wanted, they are made of metal. To save space 
the metal is thin. To separate and keep them insulated from 
each other, and to modify, owing to a most curious property, 
their storage capacity, an insulating material is placed between 




Fig. 5.— The Condenser in Section. 

them. A sheet of paper as insulator, with a sheet of tinfoil on 
each side of it, is a condenser. 

Paper is not procurable of unlimited area, and the same is 
true of tinfoil. It would also be very inconvenient to have con- 
densers as big as table-cloths. Acccordingly, to increase the 
area of the tinfoil it is piled up like the leaves of a book, with 
paper between the leaves. Ev^y leaf of tinfoil is kept in electric 
connection with the leaf once removed from it. This brings the 
tinfoil into two sets, the pieces of each set being in connection 
.with all pieces of its own set and insulated from the other set. 
The cut. Fig. 5, shows the arrangement in a diagram of its cross 
section. 

The dark lines a, a^, and a, represent one set of sheets of tin- 



ELECTRIC QUANTITY AND CURRENT. 43 

foil, all connected together. The dark lines b, &i, and ftg repre- 
sent the other set, also connected together. The shaded part 
intervening represents the dielectric, which may be paper, mica, 
or glass. In some standard condensers it is simply air, plates 
of metal being used instead of tinfoil, A and B are the con- 
ductors, by which it may be charged and discharged. They are 
twofold, so that one pair can be used for the charge and one 
for the discharge. One set of sheets receives a positive charge 
(-f) when the other receives a negative one ( — ). 

Fig. 6 shows the way a condenser is built up. It is inclosed 
in a box with bimding posts for the two sets of leaves. Various 
modifications of connections are applied in practice. 




Fig. 6. -The Condenser. 

Charging. — If electricity of one kind is poured into or over 
the surface of one set of leaves of tinfoil, the other electricity 
must be given some means of accumulating on the other leaves. 
Therefore, simultaneously with the pouring in of one kind, means 
must be provided for accumulating another kind. One must be 
poured over one set of tinfoil, and the other over the other. 

If a charge is to be given by a galvanic battery, for instance, 
its opposite terminals, A and B must be connected one to one set, 
a, a}, a^, the other to the other set, h, V, 6^ of tinfoil sheets. 
In an exceedingly short space of time each set receives its 
charge. The tinfoil being a conductor, conducts the current 
everywhere. To discharge the condenser, the oppositely-charged 
sets of tinfoil are brought into electric contact, the current passes 



44 ELECTRICIANS' HANDY BOOK. 

for an infinitesimal space of time in one direction, and then in 
diminished intensity in the other, and so beats back and forth 
lilce the swinging of a pendulum until the charge is gone, and 
the opposite electricities have combined. The quantity of elec- 
tricity which constituted the charge has disappeared. 

Meaning of Quantity of Electricity. — It would seem that 
there must be the same quantity of electricity in the condenser 
after as before the discharge. But a "quantity" of electricity is 
determinable by and recognized by its effects. The discharged 
condenser is perfectly neutral and inert, therefore there is no 
quantity of electricity in it. Keeping clear of the question of 
double or single-fluid theory, we may conclude that electric 
quantity is quite different from hydraulic quantity, which is 
gallons, liters, or other measure of a fluid. The same is to be 
said of electric current. It is far different from a current of 
water. But it is convenient to treat the electric phases of 
quantity and current as being analogous to quantity and current 
of water or steam. It is in the actions of water and steam that 
convenient analogies to electric action are found. 

Earthing a Condenser. — Another way of charging a condenser 
is to connect one set of leaves to the earth, or "earthing" it. The 
earth is arbitrarily taken as of zero potential. If one kind of 
electric excitation is imparted to the set of leaves not connected 
to the earth, the electricity of the same kind is expelled into the 
earth out of the other set. There is another way of picturing 
the action, treating the earth as an inexhaustible reservoir of 
negative electricity, ready to receive negative electricity from 
one side of a condenser, leaving it positively charged, or to pour 
in negative electricity, leaving it negatively charged. 

Capacity of Condensers. — The quantities of electricity which 
can be stored in condensers are exceedingly small. An incan- 
descent lamp may use up a coulomb of electricity every second. 
Tt would take an enormous condenser to supply it for even a 
single minute. Such condensers accordingly in practical use are 
largely employed in the class of electrical work requiring slight 
currents, such as telegraphy and telephony. The accumulation 
and instant discharging of quantity following each other in rapid 
succession play an exceedingly important role in much work in 



ELECTRIC QUANTITY AND CURRENT. 45 

modern electricity, where alternating currents accumulate quan- 
tity, discharge it, and accumulate it again twenty-five to sixty 
times in a second. This opens another field for the use of con- 
densers. The effect of the action is treated of by engineers under 
the term "capacity." 

A condenser charged with a quantity o^ electricity greater or 
less, as the case may be, can be taken away from its connections 
and carried about like a pail of water. Electricity could be 
poured out of it into another condenser, and it could thus estab- 
lish a current. The distant end of an Atlantic cable might be 
connected directly to the earth. Then if one set of leaves of a 
charged condenser were also connected to the earth, a very 
brief current could be sent through the cable by connecting the 
other set of leaves to its ungrounded near end. 

Single Surface Condenser. — A quantity of electricity can be 
accumulated and held upon any insulated conductor. A piece 
of tinfoil on the middle of a sheet of glass could be charged 
with a quantity of electricity. This would at first sight seem 
precisely the same as pouring water into a receptacle. But the 
dual element has not disappeared. The charged bit of tinfoil 
produces an opposite charge on objects around it, on the surface 
of the experimenter's skin, on the walls of the room, and else- 
where, there being theoretically no limit to the area affected. 
The little bit of tinfoil only operates as a container of electrical 
quantity in conjunction with surrounding objects. It represent^ 
one set of leaves of the condenser, the surface of surrounding 
objects represents the other set of leaves. 

Unit of Quantity. — A quantity of electricity stored in a con- 
denser is termed a charge. Poured through a conductor, it pros 
duces a current. It is thought of as a measurable thing, and its 
unit is called the coulomb. A current of one coulomb per sec- 
ond is called a current of one ampere. One coulomb at a poten- 
tial of one volt constitutes a unit of energy called the volt- 
coulomb or joule (pronounced "joioV). A joule is equal to 
nearly one-thousandth of a British thermal unit; 1047 joules have 
energy enough to heat one pound of water one degree P.; 746 
joules would exercise one horse-power for one second. 

This is not a direct way of estimating the coulomb, because it 



46 ELECTRICIANS' HANDY BOOK. 

is used as a factor of a compound unit, but energy units are so 
familiar that this method of conceiving of the value of a coulomb 
is of use. A coulomb of electricity as such is often considered as 
producing direct results. The most that can be said is that 
results follow the application of electric energy which vary in 
direct proportion with the coulombs. A coulomb without asso- 
ciation with electromotive force can do nothing, and properly 
speaking cannot be directly measured by its effects, but can be 
indirectly measured by effects which vary in direct proportion 
with eleoitric quantity. 

At Niagara Palls tons of aluminium are produced by electric 
decomposition of chemical compounds (haloid salts) of alumi- 
nium. The quantity of metal produced is due to coulombs of 
electricity passed through the fused mixture containing the 
aluminium salt or salts. An enormous number of coulombs of 
electricity are used annually in the production of aluminium. 

In electro-plating works silver is deposited in greater or less 
thickness upon tableware and other articles. The quantity of 
silver deposited depends upon the quantity of electricity used 
in doing it. One coulomb of electricity deposits 1.134 milli- 
grammes of metallic silver. It will separate from water about 
172 cubic centimeters of a mixture of hydrogen and oxygen gases. 
This gives a sort of relation between electric quantity and con- 
crete measures and weights, which makes electric quantity more 
realizable than it would be without such aids to the imagination. 

A thunder cloud as one surface, with the earth's surface and 
the surfaces of all objects thereon as the other surface, can store 
up quantities of electricity just as a condenser can. A square 
mile of thunder cloud, at such tension of electromotive force as 
to be ready to discharge a lightning stroke, need only have a 
quantity of electricity of seventy coulombs in its charge. Its 
quantity of electricity would only deposit 80 milligrammes of sil- 
ver from a plating solution. 

Coulombs of electricity forced by electromotive force through 
conductors of properly adjusted resistance produce quantities of 
heat with accompanying light, of incandescent and arc type. 
Forced through motors, quantities of mechanical energy are pro- 
duced, measured by foot-pounds or other unit. In these opera- 



ELECTRIC QUANTITY AND CURRENT. 47 

tions of electric light and power, the energy produced or absorbed 
is always expressible by a compound unit, such as the foot- 
pound. These operations are due also to a twofold action of elec- 
tricity; they are due to potential drop and to quantity com- 
bined. In the compound units, such as foot-pounds, by which 
the action of combined potential and quantity is measured, we 
discern always a potential unit, the foot for instance, and a 
quantity unit, such as the pound. To them corresponds the com- 
pound unit of electrical energy spoken of above, the volt-coulomb 
or joule, 1.356 of which are equal to one foot-pound of mechanical 
energy. 

Electric quantity can be measured by things amenable to the 
simple processes of weighing and measuring. There is danger, 
on account of this direct proportion existing between electric 
quantity and the effects of electric energy, that the agency of 
electromotive force will be overlooked. 

The coulombs passed through a decomposable solution are di- 
rectly proportional to the quantity of products of decomposition. 
But for this decomposition a fixed quantity of electromotive 
force is required. Therefore a constant value of electromotive 
force for each case accompanies each decomposition, so the nat- 
ural tendency is to leave it out of consideration, although the 
coulomb would be impotent without accompanying voltage or 
electromotive force. 

But when heat energy comes into question, the simple ratio 
disappears, and it is found that heat energy is proportional to 
volt-coulombs or joules; not to coulombs, but to coulombs raised 
to the second power. This is the reason why, in referring elec- 
tric quantity to quantities of physical energy, the joule was used 
instead of the coulomb on a preceding Hpage. 

The Storage of Quantity of Electricity involves a factor that 
applies to the storage of any physical thing, namely, capacity. 

Capacity is the relative power of storing electricity of a surface 
or combination of surfaces. 

Electricity charged upon a surface tends to escape from it and 
to join that upon the oppositely-charged surface. This tend- 
ency establishes a potential difference or electromotive force be- 
tween the two surfaces. 



48 ELECTRICIANS' HANDY BOOK. 

Capacity is defined quantitatively by means of this potential 
difference. A condenser which will hold one coulomb of elec- 
tricity at a potential of one volt has a capacity of one farad. 

It is somewhat as if we should say that a vessel which would 
hold 5270 grains of air at a pressure of ten atmospheres would 
have 1728 cubic inches capacity. The weight of the air represents 
the quantity or the coulombs, the ten atmospheres represent 
the voltage or the volts, and 1728 cubic inches represent the 
capacity or the farads. All this is simply an analogy. If the 
pressure of the air were doubled, the capacity of the vessel 
would be unchanged, but it would hold twice the quantity of air 
that it held at the lower pressure. It is manifest that the capa- 
city of a vessel could not be expressed in grains or other weight 
of air unless the pressure of the air were specified. A unit of 
capacity different from the unit of quantity is needed. 

It is exactly so with electric capacity. The potential or elec- 
tromotive force of its charge must be expressed to define the 
capacity of a receptacle of electric quantity. This is why differ- 
ent units are used for capacity and quantity. A measure of a 
capacity of one gallon holds a quantity of water defined as one 
gallon, and holds this amount under all circumstances and con- 
ditions. But an electric measure of fixed capacity, such as a par- 
ticular condenser, can hold any quantity of electricity until it 
breaks down and discharges through its dielectrics, puncturing 
them and destroying its materials of construction, if they are sus- 
ceptible of injury. 

Dielectrics. — The substance separating two oppositely-charged 
conducting surfaces is called the dielectric. It may be any sub- 
stance which will not conduct the electric current, as otherwise 
the surfaces would discharge into each other. The nature of the 
dielectric affects the operation of the condenser, and the effect 
depends on specific inductive capacity or inductivity. 

Specific Inductive Capacity or Inductivity. — The nature of 
the insulating substance or dielectric which separates oppositely- 
charged surfaces has an effect upon the voltage or potential differ- 
ence due to a charge of a given quantity. Air and gases are 
the poorest dielectrics. Sulphur is 3.2 times better than air. 
Assume two sheets of metal separated by air and brought by a 



ELECTRIC QUANTITY AND CURRENT. 49 

certain charge or quantity of electricity to a potential difference 
of 3.2 volts. If a layer of sulphur of equal thickness separated 
them, their potential difference would he only 1 volt. The rela- 
tive quality of dielectrics in this regard is called Specific Induc- 
tive Capacity, or Inductivity. 

The inductivity of some dielectrics is given here. Air, it will 
be recollected, is 1, and a vacuum about the same. 

Glass 3.0 to 10.00 Shellac 2.95 to 3.60 

Vulcanite 2.50 Turpentine 2.15 to 2.43 

Paraffin 1.68 to 2.30 Petroleum , 2.04 to 2.42 

Beeswax 1.86 Sulphur 3.20 

Mica 4.00 to 8.00 

The application of these figures is to be seen in the formula 
for calculating the capacity of a condenser. This formula for 
microfarads is 

k a 

K = 885 X 10-^° X 

X 

In this formula a is the area in square centimeters of all the 
leaves of dielectric between the conducting plates; x is the thick- 
ness of the dielectric, and k is the inductivity. 

Examples of Capacity. — The capacity of the earth is only 
0.007 farad, or 7,000 microfarads, and that of the sun is 0.076 
farad, or 76,000 microfarads. 

Polarized electrodes immersed in an acid solution have im- 
mense capacity. Two square inches of platinum electrode im- 
mersed in dilute sulphuric acid, and polarized a little over 1/50 
volt, have a capacity of 175 microfarads. This is the capacity 
of 80,000,000 square inches of tinfoil or other metal surface 
separated by Ys inch of air. If the platinum is more highly 
polarized, its capacity increases. The polarization is brought 
about by using them as electrodes for the decomposition of 
water. Hydrogen adheres to and is occluded by one plate, and 
oxygen by the other. This establishes a difference of potential 
between them. The description of Grove's gas battery given 
elsewhere may be referred to in this connection. 

nicrofarad. — The farad is too large a unit of capacity for 



50 ELECTRICIANS' HANDY BOOK. 

ordinary use, so a microfarad, or one one-millionth of a farad, 
is the standard unit. 

Current and Rate Units. — The working electrician is so ac- 
customed to deal with electricity in action, that his mind always 
turns in that direction. The mechanical engineer deals in many 
units of energy, such as the erg, foot-pound, and the like; but 
the electrical engineer instinctively refers to electricity in its 
effects. A charged condenser does not look a hit different from 
an uncharged one, though one contains potential electric energy. 

But an active conductor is surrounded with thermic and other 
phenomena in the way of force and energy, which make the 
bringing out of the recognition of its activity by the eye an easy 
matter. Current intensity is the thing most easily recognized 
and whose effects are most often witnessed. It is the production 
of current that is the end and aim of nine-tenths or more of 
engineering practice. For such reasons as the above the ampere, 
a unit of rate of quantity transfer, is far more used than the 
coulomb, a unit of quantity alone. 

The above shows the origin of a clearly discernible habit of 
thought among electricians. They do most of their work with 
rate units of quantity and of energy. Such units are for rate of 
quantity, which is current, the ampere; for rate of energy, which 
is power, the watt. 

Conductors and Non=Conductors. — The old-time division of 
substances into conductors and non-conductors of electricity had 
so much truth in it, that it is preserved to the present time. 
There is a group of substances that conduct the electric cur- 
rent well; there is another group that conduct it so badly that 
they are termed insulators and non-conductors, although every 
one of them has some conducting power. It is fair to say that 
between the two extremes thus broadly stated is a field contain- 
ing comparatively few substances. The majority of substances 
can be put into one or the other category. 

Ether Waves Produced by Electricity. — If an electric dis- 
turbance is produced, the iuminiferous ether is disturbed, waves 
are produced in it, and the disturbance is propagated through 
space. For waves to be produced in a medium, it must possess 
restitutive power. Mechanical waves can be produced in water, 



ELECTRIC QUANTITY AND CURRENT. 51 

because its particles move practically without friction between 
each other. Any disturbance rectifies itself by the particles 
working back to their original position and disseminating waves. 
The absence of intermolecular friction makes restitutive power 
possible. The force of gravity is the force called on to effect the 
restitutive action, which restores eventually to their places the 
particles disturbed by the action which caused the waves. 
Water is elastic, and without any visible disturbance can propa- 
gate waves of a totally distinct type, whose production is due 
entirely to its elasticity and not to its absence of friction or to 
its weight. Such waves are sound waves. Water conducts 
sound because its elasticity gives it the restitutive power re- 
quired for the sound wave. The elasticity of the air makes it 
also a conductor of sound, and gives it restitutive power for the 
sound wave. We can hear the hum of an insect high over us in 
the air, and hardly realize that his minute vocal organs start a 
series of waves which disturb a mass of air of many tons in 
weight. The diaphragm of a telephone receiver, acted on by a 
field due to the irregular current induced by the voice of a 
distant speaker, is forced into vibrations which reproduce the 
voice. The elasticity of the iron plate is the restitutive power 
making possible the starting of sound waves from it as a new 
center. 

Action of a Conductor. — If we use the idea of a current in 
speaking and thinking of electric action, we may picture to 
ourselves the following representation of the action of a con- 
ductor. An electric disturbance is produced in ether, and ether 
waves are set in motion. But just because the ether is restitut- 
ive, it resists the transfer of anything resembling quantity. 
Any attempt of quantity to escape from a center through the 
ether is futile. The elasticity of the ether throws it back on 
itself. 

But if a tube were opened through the ether, quantities of 
electricity could be poured through it, and the choking effect of 
a restitutive medium being removed, transfer of quantity could 
take place. This gives us the clue to a useful presentation of 
the conduction of electric quantity — of the electric current flow- 
ing through a conductor. 



52 ELECTRICIANS' HANDY BOOK. 

An electric conductor such as a wire of copper, iron, or 
aluminium, can be pictured as constituting an ether-free cylinder, 
a tube free from the restitutive ether, and quantities, such as 
coulombs, of electricity can flow through it. 

Crude as the above may seem, especially in view of the ion 
theory, it presents a useful analogy for current transmission by 
a conductor. 

Time Required to Produce a Current. — Suppose we had a long 
tube or pipe through which we began to pump a fluid such as 
water. It would take some time for the water to reach the end. 
If a current of electricity is started in a conductor which has 
some capacity, it takes a measurable time for the current to be 
appreciable at the further end, and a considerable tirhe before it 
reaches full strength at the further end. Once it has attained 
this strength, it can be maintained indefinitely. 

If the water pipe were inclined a little upward, the water 
would* take a measurable time to reach the end, and would 
reach it at first as a thin layer, and would require some time 
to be emitted in full strength. The gradual increase of fiow at 
the distant end would be still better shown by a pipe which was 
level, better yet, inclined downward. 

Let the pipe be inclined downward, and the water would 
flow under the influence of gravity. It would first trickle in 
drops or in a relatively small stream from the end, and would 
only gradually acquire the strength of the entering current. 
This strength once acquired would be maintained. 

Production of Current. — The water acts like the electric cur- 
rent in the latter case, as its entire mass is acted on by gravity. 
Every particle is pushed along individually; it is not merely 
an end push. A similar action is predicated for an electric con- 
ductor. The current is pictured as urged through it by action 
all along the conductor from the surrounding ether. An electric 
current is not due to a simple end thrust. 

Current Amperes and Coulombs. — An electric current then is 
the flow through a conductor of a quantity of electricity caused 
by electromotive force. As a current is a thing of some dura- 
tion, frequently of very long periods, we have to deflne its 
volume as it passes by us, and say it is of so many coulombs per 



ELECTRIC QUANTITY AND CURRENT. 58 

second, for instance. We can save the enunciation of two words by 
omitting "coulombs per second," and saying "amperes" instead. 
An ampere of current is one coulomb per second. If an ampere 
flows for one minute, it is the transfer of 60 coulombs; if 60 
amperes flow for one second, it is the transfer ot 60 coulombs 
also. 

The electric current is caused by electromotive force, which is 
measured by units called volts; it passes through conductors 
whose relative qualities are generally expressed by stating their 
relative resistances in units called ohms. We can have a circuit 
including an electromotive force of ten or any number of volts, 
and also any number of ohms. Such a circuit may be spoken of 
from the standpoint of electromotive force or resistance as a ten- 
volt circuit or a ten-ohm circuit, but neither epithet can be 
applied to a current. The expression a ten-volt current or a 
hundred-volt current, once so frequently used, is just as bad a 
misnomer as such expressions as a ten-ohm or a hundred-ohm 
current would be. 

Current Strength or Intensity. — The intensity of a current 
is measured and denned by the quantity of electricity it trans- 
fers in a unit of time. It is the rate of transfer of electric 
quantity. Its intensity or strength has to be measured in quan- 
tity-time units, such as coulomb-seconds, which are amperes. 
The latter word is universally used, as a ten-ampere or twenty- 
ampere current. The true conception of an ampere has presented 
such difficulty to many students that it is open to question 
whether it would not be preferable to use the double unit cou- 
lomb-second in its place. It is, of course, too late to introduce 
any such change now. 

Analogy for the Ampere. — A good analogy for the ampere is 
the miner's inch. This is a measure of rate of flow of water. 
It is in universal use in the western mining districts. It is 
the quantity of water which will pass through an aperture one 
inch square in a board two inches thick under a head of six 
inches. The cut, Fig. 7, illustrates the conditions. In one 
second a miner's inch delivers 0.1937 gallon of water, just as 
an ampere in one second delivers one coulomb of electricity. 

The head of water may be taken as representing electromotive 



54 



ELECTRICIANS' HANDY BOOK, 



force, and the obstruction offered by the limited size of the hole 
as representing resistance. 

Speed of a Current— It will now be evident how absurd is a 
question often asked: How long will it take for electricity to 
go through a wire of any given length, such as the Atlantic 
cable? The first trace of current may go through with the 
velocity of light, but it will take a measurable time for the 
current to attain sufficient strength to affect the telegraphic 
instruments in use on the line. It is not even a auestion of the 




Fig. 7.— The Miner's Inch Analogy op the Amp^b^. 



velocity of propagation of an electric disturbance— it is a ques- 
tion of charging a conductor of tangible and perhaps very great 
capacity. 

Arrival Curve.— The current's slow growth at the end of a 
long conductor is indicated by a wave-like curve. In sea cables 
this arrival curve, as it is called, is rendered more abrupt by 
the use of condensers. To illustrate how slowly a current may 
reach its full strength, the Atlantic cable worked directly may 
be cited. Starting with it uncharged and connecting it as' part 
of a circuit, 108 seconds would be required before the current 
would attain 9/10 of its full value. In 1/5 second it would attain 
1/100 of its full value. Theoretically, an infinite time would be 
required for attaining the full strength of the original current. 



ELECTRIC QUANTITY AND CURRENT. 55 

This feature of slow growth of current is greatly diminished 
in extent by the use of condensers, so that the above example is 
not a practical one. 

Direction of a Current. Memoria Te'hn'ca. — The idea of 
a moving of or transferring of electric quantity through a con- 
ductor implies a direction of the current thus formed. This 
direction has to be established on conventional grounds. To 
remember it, we may refer to the galvanic battery for a con- 
venient memoria technica. In the battery the zinc plate is the 
active one. The other plate may be pictured to the mind as 
merely gathering electricity and delivering it to the conductor. 
The current in the outer portion of a galvanic battery's closed 
circuit flows from the copper, platinum, or carbon plate to the 
zinc plate. The letters of the alphabet give the clue, as z, stand- 
ing for zinc, is the last letter of the alphabet, and the zinc is the 
last to receive the current. 

Field of Force and Lines of Force Due to Current.— The 
ether surrounding a conductor seems to play a part in urging 
a current through it. In electricity everything goes by recip- 
rocals, and a current affects the ether which surrounds it. It is 
thrown into a state of stress, circular lines of force which build 
up a sort of cylinder around the conductor being formed. 

Every impulse of electric current that goes through a telegraph 
wire produces circular lines of force around the wire, somewhat 
as if it was thickly strung with rings. This occurs for the 
whole miles of length of the wire. Once produced, the lines of 
force persist as long as the current lasts. 

Electromotive Force. — This may be defined as electric pres- 
sure which under certain conditions causes electric current. It 
is comparable to the pressure of steam in a boiler, which will 
force a current of steam through an opening, just as electro- 
motive force will force a current of electricity through a con- 
ductor. It is not energy, but appears as a factor of energy in the 
joule or volt-coulomb, and as a factor of power in the watt or 
volt-ampere. The practical unit of electromotive force is the 
volt, and the term voltage is often used as a synonym of electro- 
motive force, as is also the expression potential difference, drop 
of potential, or difference of potential. As will be seen later. 



56 ELECTRICIAN^ 8' HANDY BOOK. 

there is a distinction to be noted. Electromotive force is often 
written in abbreviated form as E. M. P. or e. m. f., an(J is often 
spoken of by these three letters. 

Production of Electromotive Force. — It is produced in vari- 
ous ways. If chemical changes are allowed to take place in 
obedience to chemical affinity, electric energy is set free, and the 
e. m. f. constituent of it is produced. Mechanical energy can by 
the dynamo- or magneto-generator be converted into electrical 
energy, and electromotive force appears. The economical pro- 
duction of electric energy, with the inevitable impressment or 
production of electromotive force, is one great object of the study 
of the electric engineer. 

Dynamic and Static Electricity. — Electricity in the mani- 
festation called a current is treated as dynamic electricity. The 
current can never exist without the coexistence of electromotive 
force. Electromotive force can exist without a current. The 
latter condition is called static electricity. 

Electromotive Force and Energy. — It is fair to say that elec- 
tromotive force is always associated with some form of electric 
energy. An instance of static electricity is a stick of sealing 
wax rubbed upon the coat sleeve. This has a very high electro- 
motive force impressed upon it, and if connected to the earth 
will produce a current. The electromotive force while in the 
static condition was a constituent of potential electric energy. 
This statement is a broad one, but expresses the general condi- 
tion, and like other broad statements may be open to some modi- 
fication. 

One of the most familiar sources of electromotive force is a 
galvanic battery. On closed circuit this will maintain a current 
due to electromotive force produced by chemical change. The 
existence in a battery of chemical combinations or substances 
whose affinities call for chemical change, shows the presence 
therein of potential energy. As long as the elements of the 
battery tend to satisfy their affinities by chemical change, so 
long will they represent potential energy and will maintain 
electromotive force. 

When the battery becomes exhausted, the chemical affinities 
no longer strive to be satisfied as before, and the electromotive 



ELECTRIC QUANTITY AND CURRENT. 57 

force disappears simultaneously with the potential energy of the 
battery. 

If the battery is on closed circuit, the electromotive force pro- 
duces a current, and active or kinetic electric energy appears. 
If the battery is on open circuit, electromotive force is still 
there as a component of inactive potential electro-chemical 
energy. 

Suppose a wire ring cut in one place were moved across the 
field of an electro-magnet. If this were done in a certain way, 
electromotive force would be impressed upon the ring. If while 
so moving its ends were tested, they would cause the reading 
of a voltmeter to show the presence of voltage on the circuit. 
The energy element of this combination is purely potential as 
long as the ring is discontinuous. A voltmeter may, as said 
above, be used to close the gap, when energy will at once ap- 
pear, because a current passes through the winding of the volt- 
meter. This is another example of the association of electro- 
motive force with potential energy. 

In the mechanical world the analogous condition obtains. It 
is hard to conceive of force except in coexistence with po- 
tential or kinetic energy. A mass of matter, a stone or weight, 
solicited by gravity represents force, and also potential energy, 
because if released it will fall and develop kinetic energy. 
But place it at the center of the earth, and it will no longer 
tend to fall; it will lose its power to produce kinetic energy, and 
it will cease to possess weight. Force will disappear because 
gravity no longer acts upon the body, and simultaneously with 
the disappearance of force, potential energy will disappear, be- 
cause the body in its new position can no longer produce kinetic 
energy. The force centered in the body disappears simultaneous- 
ly with the potential energy due to that force and to its position 
with reference to the earth. The comparison excludes cosmic 
forces; it refers only to terrestrial gravity. 

Conservation of Electricity. — ^Th€ cause of electromotive 
force is conveniently referred to the assumption that there are 
two kinds of electricity, positive and negative. Or if it is de- 
sired to avoid any revival of the old double fluid versus single 
fluid controversy, a change in nomenclature will effect it; we 



58 ELECTRICIANS' HANDY BOOK. 

may term the two kinds of electric disturbance positive and 
negative excitation or charging. A positively-charged body at- 
tracts a negatively-charged one, and in this attraction is to be 
sought the cause of current, which cause is electromotive force. 

Whenever one object is positively charged, an opposite or posi- 
tive charge is imparted to some other object or objects, which 
theoretically may be even the celestial bodies. This opposite 
charge is equal in amount, so that a sort of analogy to the 
doctrine of the conservation of energy, is found in electricity. 
The algebraic sum of the positive and negative electricities or 
electrical charges in the universe is equal to zero. 

This doctrine has been called the Law of the Conservation of 
Electricity. 

Electromotive Force and the Static Charge. — The conception 
of the necessary existence of an opposite charge for every charge 
of electricity, and of the fact that any object may act in this 
role, is very important. It tells against the conception of elec- 
tromotive force as a simple pressure or push, but suggests that 
it must operate in some way on both extremities of a circuit in 
opposite senses, or over the whole length of a conductor. Tak- 
ing an analogy from everyday mechanics, it suggests a bar 
moved in the direction of its length by a pull at one end and a 
push at the other end of the bar, given together at the same 
time. The value of this analogy is to prevent the idea that 
electromotive force acts only on the end of a conductor pushing 
electric current through it. Although the action is still the ob- 
ject of theorizing, it is certain that it is not so simple as that. 

Electromotive Force in Thunder Clouds. — When a cloud be- 
comes charged with electricity, the earth becomes charged op- 
positely. The two tend to combine, and the tendency may be- 
come so intense under enormously great electromotive force 
that the opposite electricities combine in a series of currents of 
inconceivably short duration, and which surge back and forth, 
also for an infinitesimal space of time, and constitute the light- 
ning stroke. 

There the electromotive force may mount into millions of 
volts, and project a large quantity of electricity through the 
enormous resistance of air, so as to produce destructive effects. 



ELECTRIC QUANTITY AND CURRENT. 59 

It is no trivial force that splits trees as we see them when light- 
ning has struck them, especially when we realize that but a 
small portion of the stroke may have been exerted on the tree, 
the majority expending itself on reaching the tree through the 
air. Irregular tubes of melted sand are sometimes found in 
the earth. These have been formed by the heat of the electric 
discharge of lightning. A very tangible quantity of heat is 
needed to effect the m'elting. When we realize that it is done in 
an infinitesimal space of time, it is evident that the rate of heat 
energy and of electric energy (watts) causing it is very high. 

The action of electromotive force in the disruptive discharge 
of electricity, such as that seen in the Leyden jar discharge or in 
the lightning stroke, is far different from its action in producing 
an ordinary current such as passes through a wire of an electric 
circuit. The violent discharge of the jar or of the lightning 
beats back and forth somewhat like a rebounding ball, but it is 
the same electromotive force that is operative in producing the 
minute currents that affect the telephone. The lightning dis- 
charge, with its oscillations, is comparable to the alternating 
currents of telephony somewhat as are sound waves in air to 
light waves in the ether from the standpoint of frequency. The 
two are cited as illustrations of the extremes of electromotive 
force. That of the lightning is almost immeasurable on account 
of its magnitude, that of the telephonic circuits is the same 
on account of its minuteness. A lightning stroke a mile in 
length is calculated to absorb an electromotive force of 5,000,- 
000,000 of volts, the telephone current, calculated at about 1/100 
of a microampere, requiring an electromotive force of about 
1/1,000,000 of a volt for its development. An electromotive 
force of one volt is a little less than that of a Daniell cell in 
good order. 

Electromotive Force the Cause of Current. — The electric 
current is caused to flow through a conductor by electromotive 
force. As all conductors possess some resistance, and as a con- 
stant current once started moves through each part of the con- 
ductor with equal intensity, we should anticipate that electro- 
motive force would be expended in driving the current through 
each part of the conductor. This is what actually occurs. 



60 



ELECTRICIANS' HANDY BOOKr 



Drop of Potential. — We start at the origin with a definite 
electromotive force, and it grows less and less as we progress 



along the line. Ohm's law (page 18) expressed as R 



E 



tells us 



that the electromotive force varies with the resistance. Hence 
if from beginning to end of a conductor a 
drop of 10 volts is observed, then, for every 
portion of the conductor of 1/10 its total re- 
sistance, a drop of 1 volt exists. 

Analogies of Drop of Potential. — A sim- 
ple analogy may be taken from a wire, Fig. 
8, hanging vertically from a bracket and 
subjected to twisting at its lower end. To 
show the action pointers are to be fastened 
to it at intermediate points of its length, 
projecting at right angles from the wire. 
As the bottom is twisted, each pointer turns 
through an arc. The pointer nearest the 
bottom turns through the longest arc, that 
nearest the top through the shortest arc, 
and the intermediate ones through arcs pro- 
portional in length to their distance from 
the end. If the degrees through which the 
pointers move are treated as volts, the drop 
in volts along a wire conducting a current 
is illustrated, the twist representing the cur- 
rent. 

As the degrees through which the pointers 
move grow less and less as remoter from 
the twisted end, so in a conductor the volt- 
age drops. The current is the same through- 
out it, and in the twisted wire every part 
of its length is subjected to an identical 
twisting strain. 
Another excellent analogy is shown in Fig. 9. A horizontal 
pipe conducts water. It has vertical pipes connected to it along 
its top. The height of the column of water in each of these indi- 
cates the pressure at that point. It is evident that it will be less 




Fig. 8.— Torsion 
Wire Analogy. 



ELECTRIC QUANTITY AND CURRENT. 



61 



and less as the outer end of the pipe is reached. The difference 
of height of any two neighboring water columns indicates the 
hydraulic drop, an exact analogy of the electromotive force drop. 
Electromotive Force and Difference of Potential. — There 
are two terms which are almost synonymous, yet which have a 
distinction one from the other — electromotive force and differ- 
ence of potential. If a difference of potential is maintained be- 
tween the ends of a conductor or between any two points on it, 
a current will pass. The intensity of this current can be de- 




FiG. 9.— HYDRAUiiic Analogy of Drop of Potentiaij. 



termined, the resistance of the circuit can be determined, and the 
product of the two will give the difference of potential. A suit- 
able instrument of the galvanometer type can be connected to 
the two points on the circuit, and its reading will give the differ- 
ence of potential, usually in volts, fractions of or multiples 
of volts. 

This is simple enough, A complete electric circuit may next 
be considered, consisting of a galvanic battery and an outer 
circuit connecting its terminals. The resistance of the battery 
is determined, and also that of the outer circuit. On closing the 
circuit a current passes, and its intensity is determined. On 
multiplying the sum of these resistances by the current intensity, 



62 ELECTRICIANS' HANDY BOOK. 

we have as before what appears to be a difference of potential. 
But if we try to determine the difference of potential by an in- 
strument, such as a voltmeter, we can find no two places to 
which to connect its terminals, so that it will show the difference 
of potential we have determined. Its readings are always less. 

If a number of electromagnetic lines of force are forced to 
thread themselves through a closed conducting circuit, such as a 
ring of wire, a current of electricity will pass through it as long 
as the lines of force increase or diminish in number. The cur- 
rent will continue to pass as long as any change in their num- 
ber occurs, and the more rapid the rate of change, the more in- 
tense will be the current. Multiplying the resistance by the 
current as before, we get what we might be disposed to term a 
difference of potential. But on applying our voltmeter, we can 
find no two points of the circuit between which more than one- 
half the difference of potential required to account for the 
current exists. 

The current is due to the electromotive force. If we could 
connect a voltmeter to two consecutive points of me circuit, and 
force it to indicate the difference of potential existing between 
them the long way around, we should find it equal to the electro- 
motive force. But there is no way of doing this. The term 
difference of potential always indicates the true difference exist- 
ing between points, which is the minimum one. No hypothetical 
maximum is allowed for. 

Electromotive force includes difference of potential as one of 
its phases and measures. But many cases occur in which it goes 
beyond difference of potential, and produces a current perhaps 
twice as great as could be accounted for by simple potential 
difference. 

Voltage. — This word is almost a synonym of potential differ- 
ence, except that it includes the idea of its measurement in 
volts. Applied to an open circuit, it may be identical with the 
electromotive force existing in that circuit. 



CHAPTER III. 

THE ELECTRIC CIRCUIT. 

The Electric Circuit. — The existence for any time of a cur- 
rent of electricity always implies the' existence of what is called 
a circuit. If two surfaces are oppositely charged, they may 
discharge into each other, but the discharge will last but a 
minute fraction of a second and will not be a continuous current. 
A reservation might be made in the case of a circuit actuated 
by a battery, but the electrolyte of the battery is always treated 
as a conductor. 

Constitution of a Circuit. — It consists of a conductor whose 
ends are connected when in action; when they are disconnected 
temporarily, it is an open or broken circuit. When completed 
and connected, so that it forms a re-entrant path for the cur- 
rent to flow around, it is called a closed circuit. It is called 
circuit because its ends are to be joined, making a sort of 
irregular circle, closed loop, or endless path for the current to 
go through, A straight piece of conducting material, such as a 
piece of wire or metallic rod, could be used to carry a momentary 
current or discharge of electricity, but this would not properly 
be an electric circuit. 

A lightning rod may offer a perfectly straight path for the 
discharge of a thunder cloud, and powerful electric currents may 
surge back and forth through it, currents which would make 
the metal of the rod fairly explode in a white-hot shower of 
melted metal, were they not of such inconceivably short dura- 
tion. This is a conductor only, not a circuit. 

The galvanic battery, with the conducting wire joining its 
ends in electrical bonds, gives a continuous, endless path for 
electrical action. The dynamo with its outer circuit does the 



64 ELECTRICIANS' HANDY BOOK. 

same. The telegraph system or the overhead trolley system, 
using the earth alone or in part for the return current, is treated 
as an electric circuit. The earth is taken as representing a con- 
ductor, although its function may not be strictly that of a con- 
ductor. 

Condensers jn a Circuit. — A condenser consisting of two con- 
ducting surfaces, separated by insulating material, operates as 
an absolute break in the continuity of a circuit. For a continu- 
ous direct current a condenser in a circuit would open it as 
effectually as an open switch would. Where short pulses of cur- 
rent are to be transmitted, condensers may be introduced in the 
line. This is often done in submarine cable and telegraph prac- 
tice. These break the circuit for the passage of a consecutive 
current, but the dots and dashes of the Morse code are better 




n 



Fig. 10. -Condensers in a Circuit. 



transmitted than by a through metallic connection. Such an 
arrangement, illustrated diagramatically in Fig. 10, is called a 
circuit. 

Open and Closed Circuits. — If electric conductivity exists all 
through the length of the circuit without any break, it is called 
a closed circuit. A prisoner within it would be closed in by it. 
To get out he would have to find or make an opening. An elec- 
tric circuit with such an opening is called an open electric cir- 
cuit. Once the conception of an electric circuit as a closed ring 
of conductors is formed, the meaning of open and closed circuit 
is fixed in the mind. To pull a switch away from its contact 
point, mechanically speaking, opens the switch. This opens any 
circuit of which it forms a part, and the circuit becomes an open 
circuit. If the switch is closed, the circuit becomes a closed 
circuit. 

Circuits Witliout Appliances. — An electric circuit closed and 



THE ELECTRIC CIRCUIT. 



65 



with a current passing througti it may be composed of a simple 
conductor without any generator or other appliance in it. A 
piece of wire with its ends joined, constituting a metallic ring 
or loop, may become an electric circuit. All that is necessary 
is to move it across a magnetic field of force, so as to cut lines of 
force under certain conditions, and a current will go through it, 
and it will become an electric circuit. Conditions for carrying 
it out are shown in diagram in the cut. Fig. 11. 




Fig. 11.— Ring Moving in Field of Force Under Conditions 
Producing a Current. 



Appliances and Generator in Circuits. — Current is produced in 
a circuit by electromotive force impressed upon it, and in very 
many cases a generator or several, such as dynamos or bat- 
teries, form part of the circuit. Appliances for utilizing the cur- 
rent, such as lamps and motors, may also be included. In calcu- 
lating the resistance of the circuit, all must be taken into 
account. 

A galvanic battery may be in circuit with miles of wire in 
measuring apparatus wound in thousands of convolutions. The 
battery may include a number of plates of carbon and zinc and 
half as many separate cups of solution. Or each cup may con- 
tain two solutions, kept imperfectly apart by porous diaphragms 



66 , ELECTRICIANS' HANDY BOOK. . 

or by the difference in specific gravity of the solution. Switches 
or contact plugs may come in, galvanometers or other apparatus, 
but the whole, complicated as it may be, constitutes an electric 
circuit. 

Electrolytic Conductors. — If we take the case last cited, we 
see that the current has two kinds of conductors provided for it, 
one metallic and the other liquid. Through the liquid portion, 
except perhaps for a very small fraction of the current, no ordi- 
nary conduction' of electricity takes place. As the solution is 
decomposed, electrical excitation accumulates on the plates and 
is discharged through the outer circuit by true conduction. 
Within the battery decomposition of the water group takes place, 
and electrolytic conduction takes place, something quite distinct 
from true conduction. 

An electric circuit may provide true conductors for part of 
the circuit, and electrolytic conductors for another part. 

Actions of a Circuit. — A circuit is the seat of three things- 
electromotive force, resistance, and current. The current pro- 
duced in a closed circuit by a given electromotive force is 
modified by the resistance of the entire circuit, and an identical 
current exists in all parts of it, whatever the local resistance 
may be. 

Although current is not energy, it cannot pass through a 
conductor except at the expense of energy, and whenever a cur- 
rent is passing through a conductor, energy is being expended 
therein. Every part of an active circuit is a seat of energy. 

This being the case, it follows that in every part of the cir- 
cuit electric energy disappears and some other form, usually 
heat energy, is produced in its place. If we take one point of the 
circuit as our standard of reference or point of departure, as 
we go from it we should look for a drop of some kind. The direc- 
tion of an electric current is so very hazy a conception that we 
cannot prescribe any direction in which a drop should take place. 
Abandoning a priori deductions, we can go right to the fact. 

In any portion of an active circuit we shall find an identical 
current. Between any two points of an active circuit we shall 
find a difference in potential by using any of the usual measuring 
instruments. 



THE ELECTRIC CIRCUIT. 67 

When a current is passing tlirough a conductor, the electro- 
motive force causing it is shown in the existence of a differ- 
ence of potential. The difference of potential between any two 
parts of an active circuit is called the drop or fall in potential. 

We now see how every portion of a circuit carrying a current, 
which is not energy, is a seat of energy; the drop of potential 
causing the current is the necessary element. Current multi- 
plied by potential difference is power or rate of energy, and 




Fig. 12.— Multiple Akc or Parallel C^.N-Nection. 

wherever current exists, a potential difference exists with it. 
This refers to practical conditions, not to atomic or molecular. 
Later the conception of the wattless current will be given, and 
may appear to be somewhat opposed to this statement, but the 
actual existence of a wattless current is open to discussion. 

Parallel and Shunt. — "In parallel with," "in shunt with," 
"in multiple arc," and similar expressions involving these words 
indicate a division of the conductor into two or more branches 
which reunite, so that the current is divided among them. 
"Branch" applies in the same cases. Fig. 12 shows six appli- 
ances in parallel, or in multiple arc. 

Series. — A series connection indicates that one appliance fol- 
lows another, as shown in Fig. 13. 



Fig. 13.— Series Connection. 

Series flultiple. — This indicates a connection in series of 
such groups of lamps as shown in Fig. 14. Each group has to 
pass the same current. 

Multiple Series. — This connection is shown in Fig. 15. It is 
analogous to multiple-arc connection, and each set of lamps in 



68 



ELECTRICIANS' HANDY BOOK. 



series has approximately the same drop of potential if the two 
main leads are large enough. 



Fig. 14. — Series Multiple Connection. 




Pig. 15.— Multiple Series Connection. 

Series and Parallel. — The expression three in series and two 
in parallel indicates that there are a total of 3 X 2 = 6 appliances 
arranged in two parallel series of three each, as shown in Fig. 16. 
Two in series and three in parallel indicates that six appliances 




Fig 16.— Three in Series and 
Two IN Parallel. 



Fig. 17.— Two in Series and Three in 
Parallel. 



are arranged in three parallel series of two cells each, as shown 
in Fig. 17. This class of expression can be varied indefinitely, 
as ten in series and five in parallel and the like. 

Outer Circuit means the portion of a circuit not included in an 
appliance. Thus a storage battery circuit might include a line 
of wire, motors, and lamps. The line wire, motors, and lamps 



THE ELECTRIC CIRCUIT. ,69 

would be the outer circuit; the full circuit would include them 
and the battery. 

Short Circuit. — If from one terminal of a motor a conductor 
was carried to the other, it would be a shunt for the motor, 
and if of low resistance compared to the motor, it would "short- 
circuit" the motor. A conductor of low resistance in parallel 
with one of high resistance, or in parallel with an appliance ab- 
sorbing a large drop in potential, is a short circuit for the other 
conductor or appliance, and is said to short-circuit it. 

Conductibility, Conductance, and Conductivity. — The prop- 
erty of conducting electricity is called conductibility. The con- 
ducting power of any conductor is called its conductance. The 
specific conducting power, which is the relative power compared 
with a standard, is termed conductivity. 

The conductance of a conductor depends on several things. 
The longer it is, the less will be its conductance; while the 
thicker or greater in cross section it is, the greater will be its 
conductance. Anything which lowers the conductivity of a con- 
ductor affects also its conductance, and in the same way. The 
conductivity of a conductor is its relative or its specific conduct- 
ing power as compared with other conductors. It is expressed 
on the basis of a valuation of the conductivity of the best con- 
ductor as one hundred. 

As Ohm's law was originally stated for resistance, the quality 
of conductance is little used, its reciprocal, which is resistance, 
being universally used in electrical calculations. It is a pity 
that this is the case, but units of resistance will always remain in 
use by the engineer. It has a positive action in the production 
of light and heat. Without resistance electric lamps and heating 
effects of the current would be impossible. 

Resistance. — ^Resistance is the reciprocal of conductance. It 
1 

is expressed by ;; and is a conception inferior in 

conductance 

every way to conductance, but has been so woven into the sci- 
ence that it will always be used in preference to conductance. 
No one thinks of a copper wire as an electric resister; a tele- 
graph line is not laid over miles of country to resist the passage 



70 



ELECTRICIANS' HANDY BOOK. 



of electricity. An attempt has been made to create a unit of con- 
ductance equal to the reciprocal of the ohm. It was proposed by 
Sir William Thomson (now Lord Kelvin) to give it the rather 
barbaric name of mho. In the interest of etymology it was 
fortunate that it was abandoned, as in the interest of science 
it is unfortunate. 

The negative aspect of resistance appears in its definition as 
the property of an electric conductor by which it opposes the 
passage of an electric current. Specific resistance is the rela- 
tive resistance of a material; this should be called resistivity. 
Resistance is generally used to indicate the resistance of some 

specific conductor, such as actually 
in use or liable to be employed in 
practice. 
ij Resistance and Energy. — When 

Y^\J/^y\ a current is passing through an elec- 

'" '""^^'~'^=^ trie circuit, electromotive force has 

to be expended to drive it through, 
as the resistance of the circuit op- 
poses the transmission of current, 
and the current driven by electro- 
motive force through a resistance 
indicates the expenditure of electric 
energy. The conductor of definite 
resistance through which the cur- 
rent is thus forced becomes hot, and 
this proves that energy has been ex- 
pended upon it. The energy can only 
have been obtained through the electric current and electromotive 
force. Energy results from an electric current passing through 
a resistance. If different parts of a circuit differ in resistance, 
the heating effects will be greatest at the points of greatest 
resistance. Local resistance localizes energy in a circuit. 

If a conductor through which a current is passing is immersed 
in a vessel of cold water, it will heat the water. A thermometer 
whose bulb is in the water will indicate a rise in the tempera- 
ture. The apparatus (the electric calorimeter) is shown in the 
cut. Fig. 18. 




Fig. 18.— Electric Calori- 
meter. 



THE ELECTRIC CIRCUIT. 71 

The Ohm.— This is the resistance through which an electro- 
motive force of one volt will produce a current of one ampere. 
There has been much difficulty in determining accurately a stan- 
dard. Mercury at the temperature of melting ice has been the 
conductor, and the length of a column one square millimeter in 
cross section, which would give a . resistance of one ohm, was 
determined. Four ohms came into use, of the following designa- 
tions and length of mercury column: 

True ohm 106.24 centimeters. 

B. A. ohm 104.9 centimeters. 

Board of Trade ohm 106.3 centimeters. 

Legal ohm 106.0 centimeters. 

The present standard is the International ohm, the resistance 
of a column of mercury 106.3 centimeters long at the tempera- 
ture of melting ice, which mercury weighs 14.4521 grammes. 

Mercury is " of all metals the one most easily purified, and 
being liquid is unaffected by strain. 

Internal and External Resistance. — Internal resistance is 
the resistance of a generator, whether dynamo or battery. Exter- 
nal resistance is the resistance of the portion of a circuit outside 
of the generator. 

Circuit Without Resistance. — Assume that a circuit carries a 
direct current and has no resistance. It is a purely theoretical 
conception, and at first sight seems paradoxical. It may be 
asked what would result were an electromotive force of one 
volt impressed on the circuit. The first suggestion of a solution 
would be that an infinite current would result. But an infinite 
current multiplied by finite electromotive force would give an 
infinite rate of energy, and this is absurd. The solution lies in 
a proper appreciation of Ohm's law. In it are linked together 
three factors — current strength, electromotive force, and resist- 
ance. Current strength multiplied by electromotive force is 
taken as representing rate of energy. Resistance is never absent 
from an electric circuit, and never will or can be. The unit of 
rate of electric energy made up of current strength and electro- 
motive force, and called the watt, ceases to be a unit of power 
unless resistance or its equivalent is opposed to it. A fourth 
element is omitted from the problem. In the absence of resist- 



72 ELECTRICIANS' HANDY BOOK. 

ance the current would tend to increase indefinitely. As the 
current increased, it would build up an increasing field of force 
around the conductor. Energy is required to do this, and by the 
law of conservation of energy an opposition to the increase of 
current would result. The formation of a field of force is accom- 
panied by the development of counter electromotive force, which 
is electromotive force operating in the reverse direction to the 
original. Energy is required to increase the strength of a cur- 
rent in a circuit under these conditions. The current would 
go on increasing forever, building up an increasing field of force, 
and energy would be absorbed on the circuit as long as electro- 
motive force was impressed on the circuit. 

Electrolytic Conduction. — When two plates of metal or other 
conductor are immersed in a solution which does not attack them, 
and are not in contact with each other, if a sufficient potential dif- 
ference is established between them, a-current may pass. It will 
pass if the liquid is an electrolyte. An electrolyte is a liquid de- 
composable by electricity. Even solids are supposed to some 
extent to be subject to electrolysis. Electrolytic conduction is 
conduction at the expense of the electrolyte which is decom- 
posed. 

Suppose two plates of platinum are immersed in a solution of 
dilute sulphuric acid. Let the plates be connected to the termi- 
nals of an electric circuit, and let a difference of potential be 
established between them. If the difference of potential is less 
than a volt, a very minute current will pass. Next let the poten- 
tial difference be increased. Nothing occurs until a certain 
potential difference is attained, about 1.48 volt, when suddenly a 
strong evolution of gas occurs from both electrodes and a cur- 
rent passes, which is many times stronger than the preceding 
one. 

It is unnecessary at this place to discuss the ion theory. The 
old view of electrolysis is still to be considered the practical 
one. Electrolysis is the separating of a substance into two con- 
stituents differing from each other in chemical relation. An 
electrolyte must be a compound substance. By the action of 
the current it is separated into two unlike substances. It must 
have such a composition that it can be resolved into twp parts. 



THE ELECTRIC CIRCUIT. 73 

The way the conduction takes place is thus explained: The 
solution touching one of the electrolytes gives up to it a part 
of its chemical constituents. The rest combines with the oppo- 
site constituent of the next layer of solution, displacing its simi- 
lar constituent, and this takes place all through the liquid until 
the other electrode is reached. At its surface necessarily there 
is set free the opposite constituent of the electrolyte. Such 
is the old theory, and one which holds its ground with many at 
the present day. 

Thus in the case of the acidified water, hydrogen is liberated 
at one pole, setting free oxygen. This instantly combines with 
the hydrogen of the next sheet of molecules, setting free its 
oxygen. The action is repeated until the other electrode is 
reached, at which oxygen is liberated. Exactly the quantity of 
hydrogen required by chemical laws to combine with the oxygen 
is set free. The two gases are liberated in exact chemical rela- 
tion with each other. 

If chemically-pure water is used, electrolysis will be greatly 
reduced. It is prohable that with pure water there would be 
none, but water always contains some impurity, and it is im- 
possible to perfectly purify it. We are justified, however, in 
saying that for electrolysis to take place in water, some salt or 
soluble substance must be present. 

Water containing a dissolved substance is not the only electro- 
lyte. Frequently there are substances which when melted by 
heat become electrolytes. Chlorides and fluorides of the alkaline 
and other metals are electrolytes when they are melted and are 
kept in liquid state by heat. Such electrolytes are used in the 
production of metallic aluminium by the Hall process. Prom 
such electrolytes tons of aluminium are precipitated in the works 
at Niagara Falls and elsewhere. 

Solutions of metallic salts in water form the electrolyte used for 
electroplating. The metal is deposited on the article to be plated, 
and an anode, as it is called, of the metal of the bath is often 
employed, which is dissolved and keeps up the strength of the 
solution. 



CHAPTER IV. 

OHM'S LAW. 

Three Elements in a Circuit. — There are always three things 
present or to be taken into account in considering the operation 
of an electric circuit. They are so bound up with its existence 
as known to us that we cannot eliminate any of them. The 
first one is current intensity, which is due to the second one, 
electromotive force, acting against the third one, resistance. 
They are indicated in formulas by the respective letters C or I 
for current intensity, E for electromotive force, and R for 
resistance. 

Ohm's Law, following out what has been said in the last few 
pages, is to the effect that current intensity is equal to electro- 
motive force divided by resistance. The statement expressed as 
an algebraical equation becomes: 

-I 

If the equation be taken in its broadest sense, the exposition 
of its effect just given covers it. If it be applied to a specific 
circuit, wliich therefore is of fixed resistance, it tells us that cur- 
rent intensity is proportional to electromotive force. If the volt- 
age in any part of a circuit is doubled, the current will flow with 
double intensity through that portion. 

The case may arise where a fixed electromotive force exists 
and the resistance varies. The equation states that in such a 
case the current intensity is inversely proportional to the resist- 
ance. "With a fixed electromotive force, doubling the resistance 
will halve the current intensity, and so on. 

The statement may be transformed to read thus: the resist- 



OHM'S LAW. 75 

ance is equal to the electromotive force divided by the current. 
In algebraic form this is expressed as — 

Following out the same system of interpretation, we deduce 
the facts that with constant current, the resistance varies with 
the electromotive force, and that with constant electromotive 
force the resistance varies inversely with the current, and the 
current inversely with the resistance. 

The last case represents the condition of parallel lighting 
work. By turning on lamps, the resistance of the circuit is low- 
ered. The plant we may assume to be so organized as to main- 
tain a constant voltage, therefore we know from Ohm's law 
that the more lamps we light, thereby reducing the resistance, 
the more current will be used in inverse proportion to the resist- 
ance. 

Finally, Ohm's law may be stated thus: The electromotive 
force is equal to the resistance multiplied by the current in- 
tensity, in algebraic form — 

E = RI. 

This states that with constant resistance the current intensity 
varies with the electromotive force, and that with constant cur- 
rent intensity the electromotive force varies with the resist- 
ance. 

Examples of Ohm's Law. — Assume an electroplating bath to 
be worked at a fixed resistance, and we wish to increase the am- 
perage of the current passing through it. The voltage must be 

E 

increased, because 1=—, and we have assumed that R is lu- 
ll 
variable. Assume that a number of lamps are placed in series, 
and that each one requires the same current. If the number is 
increased, the resistance of the circuit will be increased. To 
keep the current constant, the electromotive force must be 

F 

increased, because I =r — , and if R is increased, E must also be 
R 

E 

increased, or else the value of the fraction — -, and consequently 

R 



76 ELECTRICIANS' HA2^DY BOOK. 

the value of I, will change. The form E ^ R I could be well 
used here. 

An example may be given of what may be termed a fallacious 
case, where Ohm's law seems to fail but does not. 

Assume a battery of a considerable number of cells connected 
in series through a circuit of slight resistance. If the number 
of cells is doubled, and they are kept in series, the electromotive 
force will be doubled. While only a very slight increase of cur- 
rent through the circuit will be produced, yet the voltage or 
electromotive force has been doubled. 

The fallacy of the deduction that this contradicts Ohm's law 
lies in the neglect to consider the resistance of the battery. In 
doubling the number of cells, not only is the electromotive force 
doubled, but the resistance of the circuit is nearly doubled, so 
that only a trivial increase of current is produced. 

Such cases are frequent, and generally as simple as the above. 

Five Forms of Ohm's Law. — The law can be stated in five 
forms, three as given — 

E E 

I--, R = Y^ E = RI; 

and the following two — 

R- 1 I 1 

E=T^^^E = R 

The first three are those most used; the first one is more used 
than any of the others. The first group should be memorized if 
possible. 

Importance of Ohm's Law. — The consensus of opinion of in- 
structors in electrical engineering would probably be to the effect 
that good work has been done if in a three years' course Ohm's 
law is well instilled in all its bearings into the student's mind. 
It is infallible and universal; it has no exceptions. Its action 
may be limited or obscured by other reactions, but it is always 
in force in electrical circuits. It binds together firmly the three 
factors of an active electrical circuit. 

Sir Isaac Newton held when young that there should be no 
need of studying geometry; that to a properly developed mind 
it should be obvious. The simplicity of Ohm's law given in the 
three algebraic forms, with the verbal statement of each and 



OHM'S LAW. 77 

the various interpretations, tell all there is of it. But the stu- 
dent of electricity cannot exercise himself too much upon it. 
Reading over these few paragraphs should not be considered 
equal to the acquirement of Ohm's law. 

Power. —The product of volts by amperes gives the unit of 
rate of energy, which is power. From the first and third forms 
of Ohm's law we get values for I and E respectively — 

1= !i and E = RI. 

a 

Multiplying the first equation by E and the second by I, we 
have 

EI =5! and EI = RP 
R 
This gives as the expressions for electric energy: 

^, R P and E I 
R 

The first states that with constant resistance the energy rate 
or power varies with the square of the electromotive force. The 
second states that with constant resistance the energy rate or 
power varies with the square of the current. Other interpreta- 
tions less useful or at least less used are that with constant 
electromotive force the energy rate or power varies with the 
current, inversely with the resistance, and with constant current 
varies directly with the resistance. 

Examples. — To increase the energy on a circuit operated by a 
very high resistance generator or battery, the resistance must 
be lowered. Such a circuit works at approximately constant 
voltage. To increase the energy on a constant current circuit, 
the resistance must be increased. The first statement is of 
merely theoretical value, for the increase of energy will be 
through the entire circuit, and all that in the battery is of no 
economic value. Lowering the resistance in this case throws 
energy into the battery. In the other case, increasing the resist- 
ance makes the proportion of energy absorbed by the battery 
or dynamo less. 

As electric energy is distributed in practice, the law most 
quoted is to the effect that energy varies with the square of the 
current. The statement is incomplete unless it states that for 
it to be true the resistance must be constant. 



78 ELECTRICIANS' HANDY BOOK. 

The great problem which the engineer has to solve is the 
localization of energy. The energy absorbed in a battery or 
other generator is lost as far as utility is concerned. The same 
is to be said of that expended on the transmission line. 

Constant Current Circuit. — Ohm's law E ^ R 1 states that 
with constant current the electromotive force varies directly 
with the resistance. If a fixed current is passing through a cir- 
cuit, the energy rate I B in any part will be increased by in- 
creasing electromotive force expended on that part. Ohm's law 
as given above states that to increase this, the resistance of that 
part must be increased. 

But the energy localized by the increase of resistance is heat 
energy, and such energy is only desired in certain things, such 
as lamps; in motors, heating is undesirable from several points 
of view. It indicates low efficiency, and may do injury. The 
use of the drop system solves the distribution of energy for all 
cases on an active circuit, when uncomplicated by special circum- 
stances. The general law is this: Concentrate the drop of 
potential where the energy is to be utilized. A motor produces a 
drop by its counter electromotive force and resistance. The 
drop due to the first cause is useful, that due to resistance is 
useless. Energy expended on the resistance is wasted. 

A typical constant-current circuit is an arc lamp series system. 
To increase the energy rate on the outer circuit, resistance must 
be added; the more lamps there are in series, the more energy 
will be expended. To add resistance so that the energy will be 
of use, lamps are added in series. To prevent waste of energy 
on the line, it is made of size sufficient to give low resistance 
compared to that usefully contained in the lamps. 

Constant Potential Circuit. — The constant potential circuit 
is next to be considered. Let a fixed difference of potential be 
maintained at the terminals of any apparatus. The formula 

energy rate or I E = ^ states that with constant electromotive 

force the energy rate varies inversely with the resistance. To 
develop energy in any appliance whose terminals are kept at 
constant potential, its resistance must be lowered. 

A typical constant-potential system is a parallel circuit incan- 



OHM'S LAW. 79 

descent lamp system. On this, to increase the energy expended 
more lamps in parallel are put in operation, thus reducing the 
resistance. But it is interesting to note that for each number 
of lamps in operation, this becomes a constant current circuit. 
Therefore it is subject to the general law that resistance must 
be concentrated where heat energy is to be utilized. In this case 
it is in the lamps. The mains and feeders carrying the current 
to the lamps should be as large as is consistent with the re- 
quirements of capitalization. 

Drop and Fall of Potential indicate the electromotive force 
expended on any part of a circuit. Thus a 50-volt incandescent 
lamp has a drop of 50 volts when burning. The terms are 
synonyms of Potential Difference. Drop may, as in an incan- 
descent lamp, be due to resistance, or. as in an arc lamp, partly 
to counter electromotive force. 

R I Drop and Counter E. M. F.— The first is the fall in 
potential brought about by resistance. By Ohm's law such drop 
is expressed by the equation E=:RI. Without a current there 
is no R I drop; with a given electromotive force the drop varies 
with the resistance, and is equal to the product of resistance 
by current strength. This drop is to be distinguished from that 
produced by counter electromotive force. In charging a storage 
battery, each cell gives between two and three volts counter 
electromotive force, and this is almost independent of current 
strength. This produces a drop which is a counter electromotive 
force drop. 

The drop of 110 volts in an incandescent lamp is an R I drop 
as far as is known; in an arc lamp, the drop is supposed to be 
a combination of a counter electromotive force and R I drop. 

To determine the R I drop, the resistance R of the portiun of 
the circuit in which it is to^ be developed is multiplied by the 
current strength I; the result is the RI drop in volts. Thus 
the R I drop of a 220-ohm lamp passing ^^ ampere of current is 
220 X 1/2 = 110 volts. 

Examples of Power Calculations. — We have seen that the 
energy exerted by a current through a given resistance is ex- 
pressed by any of the following expressions: 

IE=^^ = RP 
R 



80 ELECTRICIANS' HANDY BOOK. 

The last expression shows that the heating or mechanical 
equivalent of a current passing through a fixed resistance is 
proportional to the square of the current. This can be very 
simply shown by assuming that lamps are to be lighted. 

Let each lamp be of 100 volts — 200 ohms standard. Such a 

f^ 1 on 

lamp will require by Ohm's law I = = 0.5 ampere of 

R - 200 

current. If we double the current, we have enough for two lamps 
in parallel. Two lamps in parallel have half the resistance of 
one lamp. To get our original resistance, we must put two 
lamps in series and two in parallel. Double the original current 
will light these four lamps, giving four times the watts as be- 
fore. By similar process we will find that to take three times 
the current without changing the resistance, three lamps in 
series and three such series in parallel will be required, giving 
nine .times the number lighted by three times the current. 
Therefore the lamps which can be lighted by currents vary with 
the squares of the currents at constant resistance. 

The lighting of a single lamp exacts a definite amperage and 
voltage. Keeping the amperage constant and varying the resist- 
ance, it is to be determined how a change in voltage will affect 
the light given on a portion of the circuit. Here the law of the 
square does not hold. If we have a 100-volt lamp requiring half 
an ampere of current and double the voltage, the lamp would 
give an immensely high illumination, and would burn out in a 
very short time. If the voltage were doubled, it would be 
necessary to take care of the increase by putting another lamp in 
series with the first. The current would remain one-half ampere, 
but for the double voltage only double the lamps would be 
lighted. 

There is no contradiction involved in these two cases. A watt 
is the product of first powers of electromotive force and current, 
and the lamps lighted vary with the watts. In the first case, by 
placing the lamps in parallel the current was increased as many 
times as there were parallel series of lamps. To keep the resist- 
ance the same, as many lamps had to be placed in series as 
were in parallel. This multiplied the voltage by a multiplier 
expressing the number of lamps in series or in parallel, both 



i 



OHM'S LAW. 81 

being the same. To get the watts expended on the lamps in the 
first case, the amperes had to be multiplied by the lamps in 
parallel to get the increased current intensity. The number of 
lamps in series gave a figure by which the voltage had to be 
multiplied to give the new voltage. Take the case of three lamps 
in parallel and three in series, and call the amperes and volts 
for a single lamp i and e respectively. The watts for a single 
lamp will then be indicated by e i. There are three lamps 
in parallel, so the new amperage will be 3 i. But there are also 
three lamps in series, in order to keep the resistance the same 
as with one lamp. The voltage therefore for the nine lamps 
arranged as described is 3 e. The product of the new voltage by 
the new amperage is — 

3ex3t = 9et, 
ar nine times the watts required for one lamp. 

Taking the expression for electric power — if it is interpreted 

R 
for fixed resistance, then the power at fixed resistance will vary 
with the square of the electromotive force. This is the case 
with the nine lamps. The electromotive force was trebled, the 
resistance was kept constant, and nine times the watts resulted. 

To keep the resistance constant, both voltage and amperage 
had to be increased in precisely similar ratio. There is no con- 
tradiction involved. 

Calculation of Resistance of Parallel Circuits. — Suppose 
three conductors each of 10 ohms resistance are placed in paral- 
lel. The combined resistance will be one-third that of a single 
circuit. A bridge three planks wide will be only one-third the 
obstacle to the passage of a crowd that a bridge one plank wide 
would be. The combined resistance of the three circuits is ex- 
pressed by 10/3 = 3.33 ohms. 

Assume that the three conductors are not of the same resist- 
ance. Let one be of 5 ohms, another of 3 ohms, and the third 
of 2 ohms resistance. The combined resistance is found by 
adding the reciprocals of the resistances and taking the recipro- 
cal of the sum. The reciprocal of a number is the quotient of 1 
divided by the number; the reciprocal of a fraction is the new 



82 ELECTRICIANS' HANDY BOOK. 

fraction having the denominator of the old fraction for numera- 
tor and the numerator for denominator. The reciprocal of 3 is 
1/3; the reciprocal of 3/4 is 4/3. The reciprocals of the resist- 
ances of the three conductors are 1/5, 1/3, and 1/2, and the sum 
of these three fractions is 31/30, and the reciprocal of this sum is 
30/31 ohm, the resistance of the parallel conductors. 

Examples of R I Drop Calculations. — The R I drop is equal 
to the product of the resistance by the current. A 16-candle- 
power lamp rated to pass % ampere of current has a resistance 
of 220 ohms, and 220 X V2 = 110 volts, which is the drop. The 
formula for the drop is E =: R I. R I drop varies with the cur- 
rent for fixed resistances. 

Take three conductors of 5, 3, and 2 ohms resistance, and 
assume that a current of 16 amperes is to pass through them. 
What is the drop? The resistance of the three parallel conduc- 
tors has been calculated as 30/31 ohms; the current is 16 amperes. 
The drop is R I = 30/31 X 16 = 480/31 =: 15.48 volts 1= B, 

By means of the drop the current passing through each one 

E 
can be calculated by Ohm's law, I = — . For the 5-ohm conduc- 

R 
tor it is 15.48/5 = 3.096 amperes; for the 3-ohm conductor, 
15.48/3 = 5.16 amperes; for the 2-ohm conductor, 15.48/2 = 
7.74 amperes. As a proof of the correctness of the figures, the 
three currents thus determined may be added, when they should 
give a sum of 16 amperes within the limits of the decimal places 
to which the operation was carried out: 3.096 + 5.16 + 7.741= 
15.996 amperes. 

Example of Counter Electromotive Force Drop Calcula^ 
tlon. — A drop may be caused by a counter electromotive force. 
One battery in opposition to another may give the latter. Sup- 
pose a battery of seventeen Daniell's cells of 1.06 volts each is 
working against a smaller battery of six similar cells, what is 
the drop? It is 6 X 1.06 = 6.36 volts, and the working electro- 
motive force on the system is equal to the difference of the elec- 
tromotive forces of the two batteries. The first battery has an 
electromotive force of 17 X 1.06 = 18.02 volts, and 18.02 — 6.36 = 
11.66 volts — the net or working electromotive force. Such a drop 



OHM'8 LAW. 83 

is usually accompanied by a drop due to resistance. The resist- 
ance drop varies witli the current; the counter electromotive 
force does not necessarily. 

Kirchhoff's Laws. — These are extensions of Ohm's law, and 
are two in number. The first states that if any number of con- 
ductors meet at a point, and if all the currents flowing to the 
point are treated as positive, and those flowing away from it are 
treated as negative, if the potential at the point remains con- 
stant, the algebraic sum of the currents will be zero. The second 
law states that in a network of conductors forming a closed 
polygon, with currents flowing through its members, the alge- 
braic sum of the products of the currents by the resistances for 
all the conductors is equal to the sum of the electromotive forces. 

Conductance and Cross=Sectional Area of Conductors. —The 
conducting power of a conductor for electricity, or its conduct- 
ance, varies with its cross-sectional area. A wire of one-tenth 
of an inch cross-sectional area has one-half the conductance of a 
wire of two-tenths of an inch cross-sectional area. This is true 
only when the wires are of the same material. Electric conduc- 
tors are generally of circular section. The areas of two circles 
of different diameters vary with the squares of the diameters. A 
wire four one-thousandths of an inch in diameter has sixteen 
times the cross-sectional area, and consequently sixteen times 
the conductance or conducting power, and one-sixteenth the re- 
sistance, of a wire one one-thousandth of an inch in diameter. 

Circular Hil System. — The circular mil system is based on 
the considerations stated above. It is a system of stating the 
size of electrical conductors, based upon the cross-sectional area 
of a standard circular electric conductor, and has obtained uni- 
versal acceptance among American engineers. 

The length of one one-thousandth of an inch is a linear mil, 
or simply a mil. The area of a circle one one-thousandth of an 
inch in diameter is one circular mil. 

The unit of the system is the circular mil. 

A wire of copper of commercial purity, one foot long and one 
circular mil in cross-sectional area, has a resistance of 10.79 
ohms at a temperature of 75° F. (24° — C.) This is a wire of one 
one-thousandth of an inch diameter. 



84 ELECTRICIANS' HANDY BOOK. 

Application. — If we know a wire's cross-sectional area ex- 
pressed in circular mils, we can determine its resistance by sim- 
ple division. Resistance varies inversely as the cross-sectional 
area of a conductor. Therefore, if the resistance of a wire of 
one circular mil cross-sectional area is divided by the circular 
mils in the cross-sectional area, of another wire of identical 
length, the quotient will be the resistance of the latter wire. 

Thus a wire one foot long and nine circular mils in area has 
one-ninth the resistance of a wire one foot long and one circular 
mil in area. In ohms the resistance of the larger wire is 
10.79/9 = 1.199 ohm. 

As the cross-sectional areas ,of wire vary with the squares 
of their diameters, a wire 3 mils in diameter has nine times 
the area of a wire one mil in diameter. 

To determine the cross-sectional area of a wire in circular 
mils, square the diameter expressed in linear mils or one one- 
thousandths of an inch. 

A wire of 1/20 of an inch in diameter is 50/1000 of an inch in 
diameter. Its cross-sectional area therefore is (50)^ = 2500 cir- 
cular mils. The resistance of one foot of such wire, if of copper, 
is 10.79/2500 = 0.00004316 ohm. 

Area of a Circular flil. • — The area of a circular mil is 
0.000000785 square inch. 

As the circular mils in the cross section of a circular wire 
are equal to the square of its diameter expressed in one-thou- 
sandths of an inch, the expression "square of the diameter" may 
be taken as the synonym of "circular mils," if the diameter is 
expressed in one-thousandths of an inch or mils. 

Examples. — Owing to the facts that commercial copper varies 
greatly in purity, and that very small amounts of impurity affect 
its conductivity to a considerable degree, there is nothing final 
about the figure 10.79 ohms given as the resistance of a foot of 
wire one circular mil in cross-sectional area. Thus Roebling 
gives 10.51 ohms, at 75° F. (24°— C.) and 10.18 ohms at 60" F. 
(15°+ C.) as the resistance of a foot of one circular mil wire. 

Accepting Roebling's figures, the use of circular mils may be 
illustrated by some calculations. 

A wire is 1075 feet long, and is 0.081 inch diameter. What is 
its resistance? 



OHM'S LAW. 85 

0.081 inch is 81 mils. A wire of 81 mils diameter has a cross- 
sectional area of (81)' = 6591 circular mils. The resistance of 
the wire is 1075 X 10.51 ^ 6591 = 18.896 ohms. 

A wire is 1100 feet long and has a resistance of 4.404 ohms. 
What is its diameter? 

Its cross-sectional area is expressed by the formula — 
1100 X 10.51 -^ 4.404 — 2625.1 circular mills. 

The diameter in one-thousandths of an inch is equal to the 
square root of 2625.1. 



V2625.1 = 51.233 mils or 0.051233 inch. 

Wire Gauges. — Various wire gauges are in use. A wire gauge 
is based upon a series of cross-sectional areas of wires. Each size 
of such wires is designated by a number. The numbers ordi- 
narily are consecutive, the lower the number the larger is the 
wire; thus No. 1 wire is larger than No. 2, and is smaller than 
No. 0. If the sizes are to be extended beyond 1, the designa- 
tions are No. 0, No. 00, No. 000, and so on. 

American Wire Gauge. — The wire gauge generally used in the 
United States for copper wire is the Brown & Sharpe gauge, usually 
written "B. & S. wire gauge," or sometimes simply "American 
wire gauge." At first sight it seems a purely arbitrary scale, but 
it is not. It is fair to assume that anyone making calculations 
of resistance of conductors will have the table to refer to. But 
there are a few figures which, if remembered, will enable one 
to operate without the table and yet to express the size of wire in 
the B. & S. gauge with a close approximation to truth. 

No. 10 wire is approximately 0.100 inch or 100 mils diameter, 
with a cross-sectional area of 10,000 circular mils. Its resistance 
per 1000 feet is 1 ohm approximately. 

The cross-sectional area of a wire of any number in the 
B. & S. gauge is approximately 1.26 times greater than the one 
below it. Thus the circular mils of No. 9 wire are equal to 
those of No. 10 wire, 10,000, multiplied by 1.26 = 12,600 circular 
mils approximately. The circular mils of No. 8 wire are equal 
to 12,600 X 1.26 = 15,876 circular mils. The circular mils of 
No. 7 wire are equal to 15,876 X 1.26 = 20,003 circular mils. All 
these are close approximations to truth. 

This brings out another feature. A wire three numbers away 



86 ELECTRICIANS' HANDY BOOK. 

from another wire has about double its cross-sectional area if of 
lower number. Thus, taking 10,000 circular mils as the cross- 
sectional area of No. 10 wire, we have No. 7 wire, three numbers 
lower. Its cross-sectional area is twice that of No. 10 wire, or 
10,000 X 2 = 20,000 circular mils. No. 4 wire is three numbers 
lower than No. 7. Its cross-sectional area is 20,000 X 2 = 40,000 
circular mils. 

From the above it follows that by going to higher numbers 
for a difference of three numbers, we must divide by 2. Thus, 
No. 13 wire is three numbers higher than No. 10. Its cross-sec- 
tional area is equal to 10 -^ 2, or 500 circular mils. No. 16 
wire is three numbers higher than No. 13 wire. Its cross-sec- 
tional area therefore is equal to 5000 -^2 = 2500 circular mils. 

These figures are only approximate, but are well within practi- 
cal limits. The following give the true cross-sectional areas of 
numbers differing by 3 and those determined by the approxi- 
mate method. 







B. & S. GAUGE. 






1. 

No. of 
Wire. 

000 


2. 

Areas la 

Cir ulnr Mils. 

True. 

168,100 


3. 

Are ! s in 
Circular Mils. 
Approximate. 

160,000 


4. 
Approx. 
-1-4 Per c( nt. 

166,400 


5. 

Errors in 

Col. 4 Per 

cent. 

1.02 


1 


83,521 


80,000 


83,200 


0.40 


4 


41,626 


40,000 


41,600 


0.06 


7 


20,736 


20,000 


20,800 


0.31 


10 


10,404 


10,000 


10,400 


0.04 




+3% 




13 


5,184 


5,000 


5,150 


0.62 


16 


2,601 


2,500 


2,575 


1.00 


19 


1,296 


1,250 


1,288 


0.62 


22 


640.1 


625 


644 


0.61 


25 


320.4 


312.5 


321.9 


0.46 


28 


158.8 


156.2 


160.8 


1.26 


31 


79.2 


78.1 


80.4 


1.52 


34 


39.7 


39.0 


40.2 


1.26 


The error in the above approximate 


process it 


will be seen 


iries from less than 2 ] 


oer cent to over 


4 per cent. 


If for wires 



OHM'B LAW. 87 

larger than No. 10, 4 per cent is added to the approximate sizes, 
and if for wires smaller than No, 10, 3 per cent is added, the 
results will be well within working limits. This is done in the 
fourth column of the table, and it will be seen that the error 
is generally less than 1 per cent. For No. 000 wire it is 1.022 
per cent; for No. 10 wire, it is 0.04 per cent; for No. 34 wire, 
it is 1.26 per cent. 

To find the size of intermediate numbers, multiply the circular 
mils of wire of any number by 1.26 to get the circular mils of 
the next larger wire. Thus, the size of No. 3 wire is obtained 
approximately by multiplying the circular mils of No. 4 by 1.26. 

41,600 X 1.26 = 52,416 circular mils, the size of No. 3 wire. 

Multiply the circular mils of wire of any number by 1.60 to 
get the circular mils of the second next wire. Thus, the size 
of No. 2 wire is obtained approximately by multiplying the cir- 
cular mils of No. 4 by 1.60. 

41,600 X 1.60 =r 66,560 circular mils, the size of No. 2 wire. 

The sizes of No. 3 and No. 2 wire given in the table are 52,634 
and 66,373 circular mils. The degree of approximation is very 
good. Especially is this true when it is remembered that no 
two samples of copper have the same conductivity, and that 
the temperature variation is considerable in copper. 

The figure 1.26 is the cube root of 2. The figure 1.60 is 1.26 X 
1.26. 



CHAPTER V. 

ELECTRO-CHEMISTRY. 

The Basis of Electro=CheiTiistry. — When one coulomb oi" 
electricity passes through water, it liberates 0.0105 milligramme 
of hydrogen. The chemical equivalent of hydrogen is 1, that of 
oxygen 16. In one molecule of water there are 2 atoms of 
hydrogen and 1 atom of oxygen, or by weight 16 parts of oxygen 
and 2 parts of hydrogen, a total of 18 parts by weight. The 
0.0105 milligramme of hydrogen was derived from a certain 
quantity of water, which bears the same proportion to 0.0105 
that the chemical equivalent of the water molecule, which we 
have seen is 18, bears to the sum of the equivalents of hydrogen 
in its molecule, which are 2. This gives us the proportion: 
2 : 18 : : 0.0105 : x = 0.0945 milligramme water. 

Hydrogen Liberated by the Coulomb. — This tells us that one 
coulomb of electricity decomposes 0.0945 milligramme of water. 
Not only is hydrogen set free, but oxygen also. The oxygen can 
be got by a similar proportion, based on the proportion of 
hydrogen to oxygen in the water molecule, which as we have 
seen is 2 to 16. 

2 : 16 : : 0.0105 : x = 0.0840 milligramme oxygen. 

This result could have been more simply reached by subtract- 
ing the hydrogen liberated from the water decomposed. 
0.0945 — 0.0105 = 0.0840 milligramme oxygen. 

Every element is liberated from a compound in strict propor- 
tion to the coulombs which pass through it by electrolytic con- 
duction. 

Proportion of Hydrogen to Oxygen. — We have seen that one 
coulomb liberates different quantities of oxygen and hydrogen. 



ELECTRO-CHEMISTRY . 89 

Hydrogen has a chemical equivalent 1/16 that of oxygen. Yet 
a coulomb liberates only eight times as much instead of sixteen 
times as much. This is because oxygen is a dyad, which means 
an element of double combining values, which is its valency, 
and hydrogen is one of single combining value, a monad. 

To get the relative amount of oxygen liberated for a given 
amount of hydrogen, we might have divided its chemical equiva- 
lent by 2, the figure of its valency, and put our second proportion 
directly thus: 

1:8:: 0.0105 : x = 0.0840 milligramme oxygen. 

Atomic Weights and Chemical Equivalents. —In any chem- 
istry will be found a table of atomic weights and sometimes 
of chemical equivalents. If the table is properly arranged, each 
element's valency will be stated. If this information is omitted 
from the table, it can be found in the text of the book. To find 
how much of any element will be separated from its combination 
by a coulomb of electricity, divide its atomic weight by its 
valency, and multiply by 0.0105. 

Electro^Chemical Equivalents. — Numbers thus obtained are 
called electro-chemical equivalents. Suppose the electro-chemical 
equivalent of nickel is required. The atomic weight of nickel 
is 58.8, its valency is 2, or it is a dyad or is a bivalent. These 
are three ways of expressing the same fact. We divide its 
atomic weight by its valency, and multiply the result by the 
electro-chemical equivalent of hydrogen: 

(58.8 ^ 2) X 0.0105 = 0.3087 milligramme 
which is the electro-chemical equivalent of nickel, or the quan- 
tity, which one coulomb can separate from a solution. 

If gold is in question, we find its atomic weight to be 197 and 
its valency 3. Its electro-chemical equivalent is given by the 
equation : 

(197 -^ 3) X 0.0105 = 0.6894 milligramme 
which is the electro-chemical equivalent of gold. 

If an electro-plater is paying for his electricity by the ampere- 
second, or, what is the same, by the coulomb, it is of importance 
for him to know how much his plating costs him in electric 
current. This he finds out from the electro-chemical equivalent 



90 ELECTRICIANS' HANDY BOOK. 

of the metal he is depositing and the total weight which he 
deposits. 

Current Strength and Chemical Decomposition. — The elec- 
tro-chemical equivalent of silver is 1.134 milligramme. If the 
strength of a current given by a battery is to be determined, it 
may be passed through a solution of silver for a known number 
of seconds. The silver which it separates is weighed, the weight 
is divided by the seconds of time during which it passed and 
by the electro-chemical equivalent of silver. The result is the 
strength of the current in amperes. 

Silver Voltameter. — The apparatus outlined above is one of 
the classics of electricity, and is known as the silver voltameter. 

Summary. —The statements just given may be conveniently 
summarized. 

The weight z of an element set free by one coulomb of elec- 
tricity, calling atomic weight A W and valency V 1, is given by 
the equation: 

z = ^^ X 0.0105 milligramme. 

A current of intensity I will deposit a weight P of an element 
per second according to the equation: 

■p = zl —- ^^ X 0.0105 milligramme. 

One ampere hour is equal to 3600 coulombs; it will therefore 
liberate 3600 X 0.0105 = 37.8 milligrammes of hydrogen, and 

^^- X 37.8 of any other element. 

This is stated very simply. Those who are interested in 
electro-chemistry should study up the theory of chemical equa- 
tions and of chemical arithmetic (stoichiometry) also. 

Example. — A chemical equation may be now written out, and 
the electro-chemical equivalents calculated. A bath of copper 
sulphate has a current of 9 amperes passed through it for 35 
minutes; how much copper and sulphuric acid will be produced? 

The chemical formula for copper sulphate is CUSO4, for sul- 
phuric acid H.SO,, for water HoO. The decomposition is ex- 
pressed by the chemical equation: 

CuSO, + H.O = Cu + H.SO, + 0. 



ELECTRO-CHEMISTRY. 91 

The nascent oxygen would usually be caused to attack an 
anode, but for our purposes we will assume that it escapes. 

The atomic weights needed are the following: Copper, Cu, 63; 
sulphur, S, 32; oxygen, O, 16; hydrogen, H, 1. Copper is a dyad. 

The copper precipitated by a coulomb is — 

Ji X 0.0105 = 0.3307 milligramme. 

35 ampere minutes is equal to 60 X 35 = 2100 coulombs. The 
35 ampere minutes will precipitate 0.3307 X 2100 := 694.47 milli- 
grammes of copper. The molecular weight of the sulphuric acid 
is obtained by adding together the atomic weights of its con- 
stituents. These weights are 2 + 32 + 64 = 98; and for every 
63 parts of copper precipitated, 98 parts of sulphuric acid are set 
free. This gives for the total sulphuric acid the proportion: 
63 : 98 : : 694.47 : x = 1080 milligrammes sulphuric acid. 

Electromotive Force in Chemical Decomposition.— Electro 
motive force does not enter into these calculations. It requires 
a definite amount of electromotive force to break up each chemi- 
cal combination. For some of them it varies exceedingly little; 
if it varied more, it could be used as a basis for methods of 
chemical separation in analysis. 

Energy in Cliemical Decomposition. — As electromotive force 
is required to break up an electric combination; and as the 
quantity decomposed or broken up varies with the coulombs, 
the energy expended varies with both these factors, and the 
energy rate or power with the volt-amperes or watts. Watts 
multiplied by seconds give volt-coulombs, and watt-seconds or 
volt-coulombs multiplied by 10,193.7 gives gramme-centimeters 
of energy. Calling coulombs Q and electromotive force E, we 
have for the energy expended in a chemical decomposition ex- 
pressed in mechanical units of weight and height: 

Q E X 10,193.7 gramme-centimeters and QE X 0.101937 = 
kilogramme-meters. 

The energy expended in decomposition is here expressed in 
pure mechanical units. The weight of substance decomposed 
by Q coulombs from what we have seen is Q z. 

The energy expended may also be expressed in heat units, say 
in grammes of water heated 1° Centigrade, or calories, some- 



92 ELECTRICIANS' HANDY BOOK. 

times called small calories. The mechanical equivalent of heat 
is 0.424 kilogramme-meter per calorie. The weight of the sub- 
stance Q z multiplied by the calories H t corresponding thereto 
and multiplied by 0.424 will give kilogramme-meters of energy, 
the expression being 0.424 Qz Ht. 

This has the same value as the other expression; they can be 
equated thus: 

0.424 Q z U t = 0.101937 Q E, 
which reduced so as to give the value of E by successive steps is — 

E = ^-^^^ z Ut = 4.16 z B.t. 
0.101937 

The above equation gives the value of E, or the electromotive 
force required to decompose a compound. We must know z, 
which is in grammes 0.0000105 (=: 0.0105 milligramme) and H ^, 
which is the heat of combination or the thermo-chemical equiva- 
lent of the compound dealt with. 

The quantities of heat expressed in thermal units are termed 
thermo-chemical equivalents. They have been determined for 
a great many chemical combinations, and are expressed in 
gramme-degrees C. or kilogramme-degrees C. The above formula 
has been deduced for gramme-degrees. It is merely a question 
of where the decimal point shall be. If the equation is to hold 
for kilogramme-degrees, it must be shifted to represent one 
thousand times the quantity; 4160 must be substituted for 4.16 
in the expression. 

Voltage Calculations. — Suppose it is asked what voltage will 
be required to decompose water. Consulting the table, we find 
that one gramme of hydrogen in burning, i. e., in forming water, 
produces 34,450 gramme-degree calories. The electro-chemical 
equivalent of hydrogen is 0.0000105 gramme. Substituting in 
the equation we have: 

E = 4.16 X 0.0000105 X 34,450 = 1.5047 volts. 

Thermo-chemical equivalents are expressed in two ways. One 
is the heat liberated by the combination of a gramme of the 
substance. The other is the heat liberated by grammes equal 
in number to the chemical equivalent of the substance. Some- 
times one and sometimes the other is given in tables. If the 



ELECTRO-CHEMISTRY. 93 

first is used in the calculation, the form of equation given for 
hydrogen is adhered to. 

B = 4.16 X electro-chem. equiv. X thermo-chem. equiv. 

If the latter is used, the factor 0.0000105 has to be retained. 
4.16 X 0.0000105 = 0.0000437. This factor may be kept as a 
constant, and we have for the second form of thermo-chemical 
equivalents : 

E 1= 0.0000437 X thermo-chem. equiv. 

Both give precisely the same result, but the second is the more 
usual and far more convenient form. An interesting point oc- 
curs in electro-plating. As each portion of metal is deposited, a 
definite quantity of energy is expended on its separation from 
the solvent. But for each such quantity of metal deposited an 
Identical quantity is dissolved from the anode, with production 
of energy. One energy is equal to the other, so that theoretic- 
ally all the energy required is that needed to overcome the re- 
sistance of the solution. In practical operation there is always a 
loss besides this. Where a metal is precipitated and none dissolved, 
the energy to decompose the salt goes to the expense account. 

Many battery calculations have been made to determine the 
voltage given by different combinations. The zinc-copper-copper 
sulphate couple (Daniell's battery) is thus calculated for its 
voltage. Zinc is dissolved, forming sulphate; this sets energy 
free or develops energy. Copper sulphate is decomposed, ab- 
sorbing energy. Zinc combining with oxygen gives out 43,200 
calories, and the oxide combining with sulphuric acid gives out 
11,700 calories, a total of 54,900 calories. These figures are for 
the gramme equivalent of zinc, which is a number of grammes 
equal to its atomic weight 65.2 divided by its valency 2, or 65.2/2 
= 32.6 grammes. 

The total calories of energy developed in calories are 43,200 -f 
11,700 =z 54,900. 

The total calories of energy absorbed by the copper separated 
from the sulphate are 19,200 + 9200 = 28,400 calories. 

The net calories developed in the combination are 54,900 — 
28,400 = 26,500. For the electromotive force we have: 
E = 0.0000437 X 26,500 = 1.15 volts. 



CHAPTER VI. 

PRIMARY BATTERIES. 

The Primary Battery Cell. — The simplest types of primary- 
battery come under the category of single-fluid cells. A piece 
of copper and one of zinc, if placed in contact with each other 
and immersed in a saline or acid solution, will generate a cur- 
rent of electricity due to the impressing of electromotive force 
upon the circuit formed hy these things — the saline or acid solu- 
tion, the copper, and the zinc. The circuit may be looked upon 
as a triangle — one side liquid, one copper, and one zinc. 

If a cartridge shell contains some dilute acid, and a wire or 
rod of zinc is immersed in it, but not allowed to touch the cop- 
per, a galvanic battery is formed. Attach wires to the zinc and 
to the copper. Connect one to a plate buried in the earth and 
the other to a telegraphic instrument, and messages can be sent 
by it over many miles of wire. There is some claim that a 
battery made out of a percussion cap has sent an electric im- 
pulse across the Atlantic Ocean. 

Three Constituent Parts. — In a cell there are three principal 
things as noted above. One is a liquid, the electrolyte, which 
will be decomposed, through attacking chemically a substance, 
almost always a zinc plate, when an electrical current is passing 
through it. The second element is the zinc plate or some 
equivalent solid or liquid material which the solution can at- 
tack. The other is a material which the solution cannot attack. 
The two materials last mentioned must be conductors of electri- 
city. 

Simple Batteries. — A glass tumbler of dilute sulphuric acid 
with a plate of zinc and one of copper (carbon or platinum and 



PRIMARY BATTERIES. 



95 



some other metals will do) dipping into it and not touching 
each other constitutes a simple battery. If the zinc is pure, no 
action will take place until the metals are connected electrically 
by touching each other or by a conductor such as a copper wire. 
When such connection takes place, a current will flow and the 
zinc will be attacked. The amount of zinc attacked will be in 
exact proportion to the coulombs of electricity produced. 

The plates of metal conduct the current by regular electric 
conduction. The liquid as such has hard- 
ly any true conducting power. A mere 
trace of conductivity can be found in it, 
by the production of very trifling cur- 
rents, practically negligible. But under the 
influence of the electric current, the liquid 
is decomposed. In its decomposition it 
virtually becomes a conductor, and is said 
to conduct electrolytically. The solution 
is called an electrolyte, which word means 
"decomposed by electricity." Such a bat- 
tery is shown in Fig. 19, in which the 
zinc plate is marked Zn, the copper plate 
Cu, and the direction of the current is 
indicated by arrows. The current, it will 
be observed, always flows from plus ( + ) 
points. 

Nomenclature. — The general nomencla- 
ture of the parts of the cell is rather con- 
fusing, but it is hopeless for anyone to 

attempt to simplify it, because positive and negative are applied 
in diametrically opposite senses to the plates, and cathode, 
anode, electrode, plate, and other terms are embalmed in the 
literature of the science. In reading an author whose subject 
is at all understood, the reader will have no trouble in appreci- 
ating the particular terminology he uses. The simpler termin- 
ology is generally the better. Any kind of ruevioria technica or 
artificial memory may be used to keep clear the distinction be- 
tween positive and negative. 

Negative and Positive Plates. — ^Writers in the English lan- 




FiG. 19.— Simple Bat- 

TEBY. 



96 ELECTRICIANS' HANDY BOOK. 

giiage usually call the plate corresponding to the copper plate 
of the simple battery described, which is the one unacted on, 
the negative plate. This is because it is not dissolved or at- 
tacked. The zinc plate, which is attacked, is then called the 
positive plate. The direction of current in the outer circuit, orf 
the telegraph line or other conductor, is taken as from the 
negative plate to the positive plate. This may be remembered 
by picturing the unattacked plate as an inert collector of elec- 
tricity, which it pours out upon the circuit in the form of current. 

The above terminology is simple and readily remembered. 

An excellent memoria technica is that the current starts from 
a plate the initial letter of whose name is generally c (carbon 
or copper) and goes through the outer circuit to a plate of initial 
(zinc). The current starts from the letter which comes earlier 
in the alphabet. 

While solid plates are almost invariably used, a liquid amal- 
gam of zinc may represent the positive plate, and liquid mercury 
might be used to represent the negative plate. There is a bat- 
tery in which the first-described arrangement exists. 

There is one term which may be advantageously used; it is 
"electrode" for plate. Thus we can broaden the assertion above 
by saying that a battery may have indifferently solid or liquid 
"electrodes." 

Cell, Couple, and Pair. — A battery of only two plates is 
called a cell, a couple, or a pair. An aggregation of cells be- 
comes a battery. It is a case of the greater including the less. 
The word pile is often applied to a battery. Properly, this term 
should be restricted to the real literal voltaic pile described on 
pages 97 and 98. 

Exhaustion and Polarization. — When the solution is weak- 
ened by dissolving the positive electrode, the battery is said to 
be exhausted. When the negative plate loses effect from accumu- 
lation of hydrogen, the battery is said to be polarized. The dis- 
tinction between exhaustion and polarization should be followed 
closely. 

Local Action and Amalgamation. — The essential thing in 
batteries is to avoid what is called local action in the 2iinc. 
Chemically-pure zinc is not attacked by dilute sulphuric acid 



PRIMARY BATTERIES. 97 

such as is used in batteries. But commercial zinc contains 
enough impurity to cause local action. This means that it forms 
a lot of little voltaic couples, and accordingly dissolves in weak 
acid. To prevent this, the zinc in all acid solution batteries is 
amalgamated with mercury. The mercury is rubbed over the 
clean surface of the zinc along with some dilute sulphuric acid. 
A strip of galvanized iron is an excellent rubber for amalgamat- 
ing. It will pick up mercury as a soldering iron will pick up 
solder. Newly-amalgamated zinc shines like silver, but soon 
loses this luster. It is exceedingly brittle. 

As a trace of zinc injures mercury, the plates should be 
amalgamated with a few drops of mercury only. Dipping them 
into mercury is unnecessary and the mercury thus abused has to 
be purified before it can be used for other purposes. 

The first genuine primary battery dates back to the Italian 
physicist Volta in 1800. This is a good starting point for the 
description of batteries. 

Volta*s Battery. — This construction goes back over a century. 
It is adapted for a series of cells in series arrangement, which 
was called a "crown of cups," or couronne des tasses. A plate 
of zinc is soldered tO' a plate of copper at one end, so that the 
two form a sort of V or U. A number of these are made. Be- 
sides these double plates, two single plates, one of zinc and one 
of copper, are provided for the ends. Cups one greater in num- 
ber than the pairs of soldered plates are partly filled with weak 
sulphuric acid. The soldered plates are put in, each pair in 
two cups, zinc in one and copper in the other, each cup receiving 
the zinc plate o* one pair and the copper plate of the other 
pair. After all the soldered pairs of plates are disposed of, the 
end cups will each have one (a) a zinc plate and the other 
(&) a copper plate in it. The whole is then completed by put- 
ting into one cup (a) a copper single plate and into the other 
cup (6) a zinc plate. Care must be taken that the plates do not 
touch. 

The electromotive force of the zinc-copper couple is less than 
one volt. It is of only historic interest. 

Volta*s Pile, or the Galvanic Pile. — A series of disks of 
copper and zinc are cut out of sheet metal. They may be some 



98 



ELECTRICIANS' HANDY BOOK. 



inches in diameter. Half as many disks of bibulous pasteboard 
or of cloth are cut out. These must be about a quarter of an 
inch less in diameter than the metal plates. The pasteboard or 
cloth disks are moistened with acid. Any excess must be 
squeezed out. A piece of heavy glass is a good basis for the 
erection of the pile. This is laid on a table or elsewhere, and 
a disk, which we will assume to be of copper, is placed upon it. 
The pile may be started with zinc. On this is placed a disk of 
pasteboard or cloth. It must not be too wet. Next comes a 
disk of 2inc, then one of copper, then pasteboard or cloth, and 







Fig. 20.— The Galvanic Pile 




Fig. 21.— The Wollaston Battery. 



BO on until fifty or one hundred plates have been used. The 
exciting solution may be water and sal ammoniac or a mixture 
of water and 1/20 its weight of sulphuric acid. The disks of 
cloth or pasteboard must not be so saturated as to permit the 
weight of the plates to squeeze out the acid. No acid must get 
upon the edges of the plates. Ears may be left on some of the 
disks, certainly upon the end ones, for attaching the wire of 
the circuit. If ears are provided on some of the interm^ediate 
plates, various voltages may be taken from it. An improvement 
is to solder the zinc and copper plates of each pair together, 
either over the entire face or accurately around the entire edge. 
The galvanic pile is mainly of historic interest. The cut, Vig. 



PRIMARY BATTERIES. 



99 



20, shows a double column or pile. The zinc plates are marked 
z, the copper plates A, the cloth u. A bar c c connects them at 
top. It will be observed that the order of copper and zinc is 
reversed in the two columns. This keeps them in the same rela- 
tion to the current. The terminals dip into two vessels of salted 
or acidulated water, & &, which can be used as terminals, by 
dipping other plates at the end of wires therein. 

Wollaston's Battery. — This is a copper-zinc combination. The 
copper plate is bent into a U shape, and the zinc plate lies within 
its bends. In the cut, Pig. 21, C C are the copper plates, Z Z the 
zinc plates, B B the cups. Blocks of wood separate the plates at 
the bottom. Their connections are screwed to a wooden bar at the 
top. This with the wooden blocks keeps 
them fixed in position. The cut. Fig. 22, 
shows the plates with their terminals O O'. 

Hare's Calorimeter. — This is another 
historical battery devised by Offershaus in 
1821 and modified by Hare in 1824. It is 
shown in the cuts. Fig. 23. A sheet of 
copper and one of zinc are wound into a 
spiral. Pasteboard strips are used to keep 
them from touching each other. They are 
dipped into a vessel of acid or sal ammo- 
niac solution when to be used. Wire ter- 
minals are soldered to the zinc and copper 
respectively. Notched standards are pro- 
vided, to carry the weight of the plates and 
to keep them out of the solution if desired. 
The zinc terminals are marked Zn and the copper ones Cu. 

Zamboni's Pile. — A glass tube one-half to one inch in diameter 
is coated on the inside with sealing wax. It is filled with disks 
of silver paper coated on tho back with powdered manganese 
dioxide rubbed up with thinned mucilage. The disks must dip 
in easily, so as not to get manganese dioxide on the inner 
surface of the tube. A pile of one thousand such pairs gives 
enough electromotive force to defiect a straw suspended by a 
silk filament. A pair of Zamboni's piles, each of some two thou- 
sand pieces of paper, are sometimes arranc'^d to attract and dis- 
charge alternately a strip of gold leaf suspended electrometer 




Fig. 23.— PiiATEs of 

VTOLLASTON'S BATTERY. 



100 



ELECTRICIANS' HANDY BOOK. 



It is said that such a pendulum will 



fashion by a filament. 

oscillate for years. 
rioderii Batteries. — We now come to batteries which are more 

than historical. Some go back to early days, but are still used 
or have been used in modern days. 
These necessarily must, if excited by 
acid, be protected against polarization. 
A general division into two classes 
may be made, single-fluid and double- 
fluid cells. We shall first consider 
single-fluid cells. 

Smee's Battery.— Zinc and platin- 
ized platinum or platinized silver in 
weak sulphuric acid. Modified by Pat- 
terson, who substituted platinized iron 
for the silver plate; by Grove, who 






Fig. 23.— Hare's Bat- 
tery. (Deflagrator.) 



Fm. 34.— Smee's Bat- 
tery. 



substituted platinized wire gauze; by De St. Amstell, who sub- 
stituted platinized tulle. Smee's battery has long been a promi- 
nent battery. The platinizing is not a simple plating with plati- 
num, but platinum black, which is a very finely divided form of 
the metal, is deposited upon the surface by electro-deposition. 
This form of platinum cannot be covered by hydrogen; smooth 



PRIMARY BATTERIES. 



101 



platinum can be covered virtually by the gas, so as to polarize 
tbe battery. As usually mounted, a bar of wood separates the 
plates, whose upper edges are secured or clamped to it. The 
exciting fluid is sulphuric acid diluted with water. It may range 
from one-seventh to one-sixteenth its volume of acid, according 
to the requirements. The platinum plate before use is dipped 
every day into a solution of ferric chloride. This oxidizes any 
reduced deposit or occluded hydrogen. Silver-plated lead plati- 
nized is substituted sometimes for the regular negative electrode. 




Fig. 35.— Smee's BATrBBY— Tter's Form. 



E. M. F., 0.42 to 0.47. This construction is shown in Fig, 
24. Another form is shown in Fig. 25. Mercury is poured into 
each cell, and bits of zinc are dropped into it from time to time. 
Thus scraps of zinc can be used instead of a plate. A ball of 
zinc, cast on the end of a wire, which wire must be insulated, 
dips into the mercury. Walker (1859) used platinized carbon 
instead of platinized metal. E. M. F., 0.66. 

Iron Negative Plates. — Sturgeon (1840) used cast iron; Miin- 
nich (1849) amalgamated iron; Callan (1845) cast iron in form 
of a shallow vessel, constituting at once the recipient for solution 
and the negative electrode. Hughes (1880) used zinc-hydrogen- 
ated iron, acidulated water; polarization only one-fifth that of 
Smee's battery. E.M.F., 0.56. 

Aluminum Negative Plate.— Helot (1855) zinc-aluminium- 



102 



ELECTRICIAN t^' HANDY BOOK, 



dilute sulphuric acid. The aluminium negative plate is dipped 
in strong hydrochloric acid for a few minutes to make it less 
easily polarized. 

Grove's Battery (1838). — Zinc amalgam-platinum in a solution 
of sulphuric acid with nitric acid as a depolarizer. This has 
seen long service as one of the leading batteries of the world. 
The cut. Fig. 26, shows one construction. The platinum goes 
in a porous cup, V. This contains nitric acid, 1.33 sp. gr. Outside 
the porous cups is the zinc, Z, and the whole is contained in a 
battery jar charged with sulphuric acid. As it produces current 





Fig. 26.— Grove's Battery. 



Fig. 27.— Grove's Battery. 



the nitric acid is reduced, and corrosive and poisonous fumes of 
nitrogen oxides are evolved. It is credited with an electromotive 
force of 1.9 volts. Generally, less than this is to be looked for. 

Another form of Grove's battery, in which a bent platinum 
plate is used to increase the area and diminish the resistance, is 
shown in Fig. 27. 

Various modifications have been tried. Oxalic acid (Royer) 
has been used instead of nitric. The result was the production 
of formic acid with evolution of hydrogen. A saturated solution 
of ferric chloride with a little nitric acid has been recommended. 

As long ago as 1840 (Hawkins) and 1841 (Olfers) the platinum 
was replaced by iron in concentrated nitric acid. Iron is not 
attacked by this acid when concentrated. The acid if diluted 



PRIMARY BATTERIES. 103 

attacks it, so this formed an objection to its use, as the acid soon 
becomes dilute by use of the battery. 

Uelsmann proposed to substitute silicon iron for platinum in 
the Grove cell. The E. M. F. varied with the concentration of the 
nitric acid. 

Buff (1857) proposed aluminium in place of the platinum. 

Grove himself in 1839 had tried wood charcoal and retort 
carbon as substitutes for platinum. It is said that he thought 
that in the scientific world platinum only would be considered 
"truly in harmony with science." 

Callan (1847) substituted platinized lead for the platinum, and 
replaced the nitric acid by a mixture of 4 parts concentrated 
sulphuric acid, 2 parts nitric acid, and 2 parts saturated solution 
of potassium nitrate. 

Carbon Negative Plates.— Early in the last century Gautherot 
found that wood charcoal would act as a negative electrode in 
Volta's battery. The early inventors in this line were Leuch- 
tenberg (1845), Fabre de Lagrange (1852), J. Walker (platinized 
carbon) (1859). 

Tommasi (1881) used zinc-graphite in dilute sulphuric acid. 
The graphite is heated to redness, and cooled in a current of car- 
bon dioxide or nitrogen. E. M. F. at first, 1.37 volts; falling 
rapidly to 1 volt, and after a few hours to 0.83 volt. 

Moving Electrodes. — A number of batteries have the plates 
moved in and out of the solution, so as to depolarize the negative 
plate. BecQuerel (1852) was an early investigator in this line. 
Erckmann made his plates disk-shaped, mounted them on an axle, 
and rotated them. About half their depth was immersed in the 
acid. Brushes rubbed against the plates as they rotated. Maiche 
(1864) devised a copper- or carbon-iron couple with very dilute 
nitric acid (one per cent). The copper or carbon electrode was 
disk-shaped and rotated as in Erckmann's battery, with about 
one-third its area immersed. Skene and Kuhmaier used a zinc 
copper cell with dilute sulphuric acid; the copper is moved in 
and out of the liquid by clockwork. 

Bunsen's Battery (1842).— Amalgamated zinc carbon in dilute 
sulphuric acid mixed with fuming nitric acid as depolarizer. 
Bunsen improved on Grove's cell by substituting relatively cheap 



104 ELECTRICIANS' HANDY BOOK. 

« 
carbon for platinum. E. M. F., 1.89 volts. He placed the zinc in 
the porous cup and the carbon in the exterior vessel. Archereau 
reversed the relation of the plates, and put the carbon in the 
porous cups and the zinc outside. The battery has been elabo- 
rately tested by Meylan (1886) with the following results: 

Exciting liquid, sulphuric acid consisting of equal volumes of 
60° Beaume sulphuric acid and water. Depolarizer, nitric acid 
of 36° Beaume. Zinc, active surface 116.25 square inches. E'x- 
ternal resistance, 1.27 ohms. Internal resistance, 0.04 ohm, 
falling to 0.035 ohm and rising to 0.12 ohm. 

Electromotive force. Current. Energy. 

Starting 1.93 volts. 

After 15 minutes closed circuit 1.87 " L42 ampores. 

" 24 hours " " 1.77 " 1.33 '• 56 watt hours. 

" 30 " " '' 1.73 " l..t '' 70 

A modern Bunsen battery is shown in Fig. 28, the carbon and 
zinc plates being indicated by C and Z, and positive and negative 
by the regular signs + and — . 

The Bunsen and Grove cells have the advantage that no salts 
are used in their solutions, so there is no trouble with crystalli- 
zation in the carbon or platinum compartment. The evolution of 
nitrous fumes corroding the battery connections and exacting 
special ventilation is a very bad feature. 

Modifications of Bunsen's Battery. — Numerous attempts have 
been made to modify it. A few only will be mentioned here. 

Liais and Fleury (1852) made a carbon cup act at once as the 
porous cup and as the negative electrode. The nitric acid was 
poured into its interior. Miergles (1868) and Faure (1880) pro- 
posed a stoppered carbon bottle to hold the nitric acid and act as 
negative electrode. Boettger (1868) used carbon soaked in nitric 
acid as negative electrode. To suppress the fumes of the depo- 
larizer Balsamo advised maintaining a layer of turpentine on 
top of the nitric acid. This suppresses a great deal of the emana- 
tion and suffers change in its own composition. Archereau sug- 
gested the use of tin scrap contained in a vessel inverted over the 
cell to combine with the nitrogen oxides. Rousse used a layer 
of oleic acid to absorb the fumes. Thann used as depolarizer a 
mixture of 500 grammes nitric acid to 60 grammes chloro- 
chromic acia (Cr^ O, Cl^). The latter is obtained by acting on 



PRIMARY BATTERIES. 105 

10 parts potassium bichromate and 17 parts of sodium chloride 
with 30 parts concentrated sulphuric acid. It absorbs the nitro- 
gen oxide fumes. 

Gibbs* Battery.— Prof. Wolcott Gibbs in 1878 produced a truly 
philosophical modification of the depolarizing liquid in the Bun- 
sen battery. He used as depolarizer nitric acid of 1.4 sp. gr. 
saturated with ammonium nitrate. This solution gives off innoc- 
uous nitrogen, as it is reduced by the nascent hydrogen. 

Poggendorff*s Battery. — This is one of the leading batteries. 




Fig. 28.— Bunsen's Battery. 

It resembles closely the Bunsen battery, and dates back to 1842, 
the same year that Bunsen's battery is referred to. It is a zinc- 
carbon couple with porous cup and as an exciting liquid salt solu- 
tion or dilute sulphuric acid. Its depolarizer is a solution of 
potassium bichromate. The latter oxidizes the nascent hydrogen, 
so as to prevent depolarization, and gives off no gas or fumes. 

By using dilute sulphuric acid as the excitant, and a strong 
solution of potassium bichromate in dilute sulphuric acid as the 
depolarizer, an electromotive force of 2 to 2.2 volts is obtained. 

The next cut. Fig. 28, serves as a representation of the Poggen- 



106 



ELECTRICIANS' HANDY BOOK. 



dorff battery. There is no material difference of construction 
between them, and Poggendorff' s battery is often called Bunsen's 
battery. 

Sometimes the Poggendorff battery is made up without the 
porous cup, as in the Grenet battery described further on. The 
zinc and carbon are immersed in the same solution. A mixture 
of sulphuric acid, water, and potassium bichromate in solution 
forms at once the exciting and depolarizing solution. This 
solution acts upon the zinc disadvantageously. 

For all purposes, where a powerful battery is needed and 
where constancy is less desirable than 
power in small compass, some form of 
the Poggendorff or bichromate couple is 
very available. 

The disadvantage of the omission of 
the porous cup is the dissolving of the 
zinc on open circuit, even if amalgam- 
ated. The combined depolarizing and 
exciting fluid attacks the zincs under the 
above circumstances. This difficulty is 
met by withdrawing the zincs from the 
solution' when the battery is not in use. 
A great variety of this class of battery 
differing in mechanical details has been 
devised. 

Modifications of Poggendorff»s Bat= 
tery. — Some representative batteries of the Poggendorff porous 
cup type are the following: 

Fuller's flercury- Bichromate Battery is shown in Fig. 29. 
The zinc electrode in the shape of a cone or pyramid is cast 
around the lower end of a copper wire, which must be insulated. 
It rests on its base in the bottom of the porous cup. It is in 
height but a fraction of the height of the cup. Mercury is poured 
in to the porous cup, so as to lie in contact with the zinc to keep 
it amalgamated. The carbon electrode is in the outer vessel. 
In the illustration, Fig. 29, Z indicates the zinc electrode. The 
porous cup receives the acid solution; the depolarizing solution 
is in the outer vessel. In starting, no acid need be put into the 




Fig. 29. 



-Fuller's Bat- 
tery. 



PRIMARY BATTERIES. 



107 



porous cup. Enough will soon find its way in from the depolarizer 
to start the cell to working. 

It is claimed that on an ordinary working circuit this battery 
can be run for six months without renewal. The internal resist- 
ance can be varied, as in any other porous cell battery, by using 
porous cups of varying thickness and porosity — y^ ohm to 4 ohms 
are given as ranges of resistance of the commercial cell. It has 
been used in England extensively for telegraphic service. 

Camacho Cascade Battery.— This battery provides for the 
constant renewal of the bichromate depolarizer. The cut. Fig. 30, 
shows a series of cells arranged on steps. The depolarizing solu- 
tion is caused to flow slowly from the upper vessel into the porous 
cup of the upper cell. Thence by a pipe it flows from the bottom 




Fig. 30.— Camacho's Cascade Batteby. 



of this porous cup into the porous cup of the next lower cell. 
This flow goes through as many cells as desired. 

Baudet Siphon Battery. — In this construction the regular por- 
ous cup construction is used. Siphons with india-rubber starting 
bulhs connect the outer cups of contiguous cells. The zinc plates 
are contained in the porous cups. The depolarizing fluid, when 
all the siphons are charged, will siphon from one cup to the next 
as long as a difference of level obtains between the liquid in the 
first cell and the outlet of the siphon connected to the last. 
Depolarizing solution is slowly admitted to the first cell, and 



108 



ELECTRICIANS' HANDY BOOK. 



siphons along the row, to the end one. The effective level of the 
outlet siphon of the last cell can be adjusted by a trap, which 
also keeps the siphon charged. 

Radiguet Battery.— In this battery the zincs are in the porous 
cup. The porous cup forms one division of a double vessel, some- 
what heart-shaped in contour, whose other division is glazed. 
The combined glazed and porous cup oscillates about a journal. 
When tilted in one direction, the porous division descends into 
the main battery cell, and the acid runs from the glazed division 
into the porous one. The zinc plate is fixed in position in the 
porous cup division. When the combined cell is tilted in the 
other direction, the porous cell division is withdrawn from the 
main battery cell, and the acid runs out of it 
into the glazed division. 

The effect of this is that when the battery is 
not in use, the zinc is out of contact with acid, 
and the acid solution is in a separate impervious 
receptacle away from the depolarizing solution. 
The latter is in the main cell with the carbon. 
A single motion of the lever or handle turns 
the porous cup down with the zinc in it, into 
the depolarizing solution, and the acid simul- 
taneously flows in and surrounds the zinc. 

Other modifications of the Poggendorff cell 
show the dip battery principle applied to the 
zinc plates — the carbons being left immersed. 
The porous cell being only an imperfect expe- 
dient, this withdrawal of the zincs leaves the 
solutions to intermingle by diffusion through 
the pores of the porous cup, so this withdrawal 
of the zincs is only a partial solution of the problem. 

Grenet's Battery.— In this battery, shown in Fig. 31, the zinc 
plate, Z, is drawn out of the solution by the handle a when the 
battery is not in use. This cell is variously constructed on the 
general lines shown. 

Dip Batteries.— Many bichromate batteries are mounted so as 
to have all their plates withdrawn from the solution. All the 
plates are attached to a bar by which they are all raised simul- 




FiG. 31. -Grenet's 
Battery. 



PRIMARY BATTERIES. 109 

taneously from the liquid. A sort of windlass is often mounted 
on a frame to effect the lifting. 

Partz's Battery utilizes the different specific gravity of the 
liquids. The carbon lies horizontally on the bottom; the zinc, 
also horizontal, is suspended above it half way up the jar. It 
is first charged with a solution of magnesium sulphate 1:4, or 
ammonium chloride 1:5, or some similar salt. Five per cent to 
ten per cent of hydrochloric acid may be added to reduce the 
resistance, but it exerts local action upon the zinc. A solution 
of sulphuric acid and chromic acid is poured in through a glass 
tube, which reaches to the bottom of the vessel. This depolariz- 
ing solution of high specific gravity lies under the other solution, 
fioating it up and covering the carbon. As the depolarizer is 
exhausted, more is added through the tube. This battery is 
credited with over 2 volts E. M. F. 

Depolarizing flixtures and Exciting Solutions in Batteries 
of the Poggendorff Type. — The Bunsen battery carrying out the 
principle of Grove, but substituting carbon for platinum, opened 
the possibility of new depolarizing solutions. Many such, which 
would attack platinum, are available for carbon. Poggendorff's 
substitution of chromic acid for nitric acid did away with nitrous 
fumes. A number of solutions for carbon-porous cup batteries 
have been tried, and many are of interest. 

D'Arsonval (1881). — A depolarizing mixture of 1 volume nitric 
acid, 1 volume sulphuric acid, and 4 volumes water saturated 
With copper sulphate was employed by him. 

Ruhmkorff (1867) and Dupre (1885). — Carrying out a sugges- 
tion due to the earlier scientist, Dupre used as polarizing solution 
a mixture of water 600 parts, sodium nitrate 510 parts, potassium 
bichromate 60 parts, and sulphuric acid 720 parts. The potas- 
sium bichromate absorbs the nitrogen oxides. 

Mauri. — His depolarizer consisted of potassium chlorate 50 
parts, potassium nitrate 25 parts, mercuric chloride 4 parts, 
iodine 5 parts. 

Koosen (1873). — His depolarizer was based on the use of potas- 
sium permanganate. Two solutions are described: a, potassium 
permanganate 300 parts, sulphuric acid 100 parts; h, potassium 
permanganate 100 parts, sulphuric acid 250 parts. Water enough 



no ELECTRICIAN^^ HANDY BOOK. 

to dissolve the potassium salt is used. It must be mixed with 
great care, the acid being added little by little to the aqueous 
solution of permanganate. E. M. F., 2 to 1.7 volts. 

Lacombe. — Saturated solution of potassium chlorate and ferric 
sulphate or chloride, to which is most carefully added sulphuric 
acid. Potassium permanganate may be substituted for the 
chlorate. 

Duchemin. — Picric acid solution mixed with sulphuric acid 
was employed as a depolarizer. It is reduced to picramic acid. 
flixture of Sulphuric and Nitric Acids.— Many depolarizing mix- 
tures were made by mixing these two acids. The idea was to 
have the water combine with the sulphuric acid, so as to give 
a stronger nitric acid to do the depolarizing. 

Potassium Bichromate Solutions. — Formulas. — Poggendorff. — 
Potassium bichromate 100 parts, water 1000 parts, sulphuric acid 
50 parts. 

Delaurier. — Potassium bichromate 18.4 parts, water 200 parts, 
sulphuric acid 42.8 parts. 

Chutaux. — Potassium bichromate 100 parts, mercury bisul- 
phate 100 parts, water 1000 parts, sulphuric acid 66° (B.) 50 
parts. 

Dronier's Salt. — A mixture of one-third potassium bichromate 
and two-thirds potassium bisulphate. It is dissolved in water 
just before use. 

Tissandier. — Potassium bichromate 16 parts, water 100 parts, 
sulphuric acid 37 parts. Finely-pulverized bichromate is used. It 
is dissolved as far as it will in the water heated to about 100° F. 
The acid is then added, and the mixture shaken until all dis- 
solves. 

Kookogey. — Potassium bichromate 227 parts, boiling water 1134 
parts, sulphuric acid added while water is at boiling temperature 
1588 parts. It is allowed to cool, and the liquid is decanted from 
the crystalline residue which forms on cooling. 

Trouve's. — Water 80 parts, pulverized potassium bichromate 12 
parts, concentrated sulphuric acid 36 parts; all parts by weight. 
The pulverized potassium bichromate is added to the water, and 
the acid is added slowly with constant stirri'ng. As much as 25 
parts potassium bichromate may be added to 100 parts of water. 



PRIMARY BATTERIES. Ill 

The heating produced hy the acid and water dissolves nearly all 
the potassium salt. Use cold. 

The Daniell Battery.— The Daniell battery is the type most 
used probably of all primary batteries. It is of low voltage, a 
little over one volt, and of high resistance, several ohms in all 
ordinary sizes. Its great constancy and cheapness of its first 
cost and of its solution have made it the telegrapher's battery 
par excellence. It is being replaced by caustic potash and other 
batteries to some extent. 

The typical cell contains a porous cup for the zinc. It is filled 
with water. A copper plate is placed outside the porous cup, vir- 
tually surrounding it. A pocket or receptacle for copper sulphate 
crystals is provided near the top of the copper plate, and is often 
made out of the same copper as the plate. Sometimes to start it 
off some salt, sodium sulphate, or zinc sulphate is added to the 
water. 

Daniell produced the cell in 1836. Tommasi gives the invention 
to Becquerel in 1829. Walker in 1830 made a similar couple, 
using animal membrane for a diaphragm instead of unglazed 
porcelain for the porous cup. 

The action of the cell is this: The copper sulphate dissolves. 
Its sulphuric acid attacks the zinc, its copper is deposited as 
metal on the copper plate. The fluids move by or move through 
the porous cup. Under the action of a current, on closed circuit, 
the level of the copper sulphate solution rises. 

The action of this battery is subject to the defects of all porous- 
cup batteries. The solutions mix through the diaphragm so that 
the depolarizing solution comes into contact with the zinc. This 
is very injurious because the metallic copper precipitates on the 
zinc. This is done at the expense of the zinc, which is dissolved, 
constituting a source of expense. The dissolving of the zinc 
increases the specific gravity of the solution, which has to be 
* weakened sooner than would be the case without this wasteful 
dissolving. The zincs have to be scraped occasionally, to free 
them from the copper. Both the latter features of wrong action 
involve extra labor. 

The electromotive force varies slightly according to the salts 
present in the zinc compartment and with the presence or absence 



112 ELECTRICIANS' HANDY BOOK. 

of free acid. The great constancy of this battery has made it in 
the past a favorite for testing purposes as a standard of electro- 
motive force. Scientific investigators have made many investiga- 
tions of its reactions and determinations of its electromotive 
force. The latter varies from 1.160 to 1.03 volts. 1.07 volts is 
usually taken as the electromotive force. 

The chemical reactions involved are put thus: For the vessel 
containing the zinc plate: 

H, SO, + Zn = ZnSO, + 2H. 
For the vessel containing the copper plate: 
2H + Cu SO, = H^SO, + Cu. 
The electromotive force is but slightly affected by heat. If 
the surface of the copper is oxidized, its voltage is slightly 
increased by light. Dilution of the solutions is almost without 
effect on its voltage. The quality of the metals in the electrodes, 
whether rolled or rough, crystalline or not, makes very little 
difference in the voltage. 

The resistance of the Daniell cell is said to depend more upon 
the area of the copper than on that of the zinc. Amalgamation 
of the zincs is not favored by all investigators. Different mate- 
rials for the diaphragms have been tested, and have naturally 
been found to have no influence on the electromotive force. 

riodifications of Daniell's Battery. — These are not so numer- 
ous as might be anticipated, unless we include the gravity cells. 
Varley proposed to surround the porous cup with a layer of zinc 
oxide. This will decompose any copper sulphate which works its 
way through the walls of the porous jar. Copper oxide will be 
precipitated, and zinc sulphate will be formed. One great annoy- 
ance is the deposition of metallic copper on the porous cup's 
exterior. Borseul wound a spiral copper wire around the .cup 
with a spiral plate at its lower end, the middle of the wire at- 
tached to the copper plate. The wire was supposed to catch all 
the copper as it precipitated. 

Parelle and Veritee, in their balloon or flask battery, place 
the copper sulphate in a glass flask with narrow neck, as shown 
in Fig. 32. It is filled with water, and inverted neck downward 
into the porous cup. It supplies copper siilphate for a long time. 



PRIMARY BATTERIES. 



113 




Fig. 33.— Balloon or Flask Battert. 



The solution in the outer jar must he weakened from time to 

time; otherwise, the hattery 
takes care of the solution au- 
tomatically. 

Trouve's blotting-paper bat- 
tery, shown in Fig. 33, con- 
tains a copper and a zinc plate 
marked Cu and Zn. The space 
between is filled with disks 
of blotting paper. The lower 
sheets of paper to one-half 
the total number are soaked 
in copper sulphate solution 
and allowed to dry. An insul- 
ated copper wire runs down 
through a central hole to the 
copper plate and is soldered 
thereto. Another wire is con- 
nected to the zinc plate. When 
the battery is to be used, 
water is poured upon the disks until it shows at the edges; they 
are pressed together and placed in the jar. This battery will 
give a small current 
for months. 

Eisenlohr (1849) used 
a sodium or potassium 
bitartrate in the zinc 
division. Buff used 
liquid zinc amalgam. 
An insulated wire runs 
down through the solu- 
tion into the mercury. 
GaifCe's cell is a com- 
bination gravity and 
porous cup cell. The 
zinc is in the shape of 

a cylinder, and is suspended from the edge of the jar near 
its top. The porous jar is glazed or treated so as to be im- 




FiG. 33.— Trouve's Blotting-Paper Battery. 



114 ELECTRICIANS' HANDY BOOK. 

pervious for its lower half. It contains the copper plate, and 
a wire extends from the copper plate up over the edge of 
the porous cup and down to the bottom, where it is carried 
around the lower part of the half porous cup in a circle. 
Any copper sulphate in the porous jar as it works its way 
through descends on account of its specific gravity to the 
bottom of the outer jar. When the circuit is closed, this cop- 
per sulphate is the first decomposed, and the copper ring acts 
as an electrode. When this part of the solution is exhausted, 
the copper in the porous jar becomes the negative electrode. 
Then the cell works like a regular Daniell's battery. This 
construction favors the preservation of the zinc from local action 
or attack by the copper sulphate solution. 

D'Arsonval (1881) has, by using caustic soda solution in the 
zinc compartment, brought up the voltage to 1.5 volts. 

Reynier reached the same voltage, using a seamless bag of 
parchment paper for the porous cup, a 30 per cent solution of 
caustic soda for the zinc compartment, and sodium bisulphate or 
sulphuric acid in the copper sulphate solution. He used other 
mixtures, whose complication tends to exclude them from every 
day use. 

Sand Type of Daniell's Battery. — Several cells have been de- 
vised in which a layer of sand replaces the porous cup. Minotto 
(1863) uses sand, D'Arsonval uses animal black or bone black, 
Coronat uses sawdust. There are other modifications. 

Gravity Battery. — This term is almost restricted to one type 
of cell, the copper-zinc-copper sulphate couple. It is based on the 
exact reactions of the Daniell cell, but has no porous cup, relying 
entirely on the various specific gravities of the constituent 
liquids to keep them separated. The construction of the modern 
gravity battery is .cheap, because the porous jar is dispensed with. 
The original gravity battery dates back to 1859, when it was pro- 
duced by Meidinger. There is apt to be a little uncertainty about 
the originators of fundamental things in the world of practical 
science, but this inventor going back nearly fifty years has given 
his name to the gravity battery, and the title adheres to it still. 

Meidinger's Battery (i859). — The cup was contracted in diam- 
eter at about one-third of its height, so as to form a shoulder, on 



PRIMARY BATTERIES. 115 

which a cylinder of zinc rested. A smaller cup rested on the 
bottom of the main cup, and contained the copper electrode. This 
cup held strong copper sulphate solution, whose high specific 
gravity operated to prevent it rising and attacking the zinc when 
on open circuit. A glass tube with a hole in its bottom was 
arranged to keep up the strength of the copper-sulphate solution. 
A flask such as shown in Fig. 32 is sometimes applied to this 
battery. 

The next steps in the development of this cell were in the 
direction of simplification, and in modern cells there are often 
only three parts, twO' electrodes and the jar, A copper electrode 
which rests on the bottom of the jar, a zinc electrode of approxi- 
mate disk shape supported in a horizontal position near the top, 
and the battery jar are the three parts. To charge it, the copper 
electrode is put into the jar, resting on its bottom, and crystals 
of copper sulphate are introduced to a depth of two inches or 
more. It is then carefully filled with water to within an inch of 
the top. The solution of copper sulphate is of higher specific 
gravity than water, and stays at the bottom more or less com- 
pletely, especially if the battery is in use. But if the battery is 
little used and remains on open circuit, most of the time the 
copper sulphate solution rises and acts upon the zinc, attacking 
it, depositing metallic copper upon it, and impairing rapidly the 
condition and efficiency of the battery. 

The zinc dissolves, forming zinc sulphate, whether the battery 
is working or not. In the first case, the zinc should and must 
dissolve; in the second case, when the battery is not working, the 
solution is due to local action and is a defect. The inevitable 
formation of zinc sulphate acts to increase the specific gravity of 
the overlying solution, and to diminish the characteristic gravity 
feature of the cell. Accordingly, from time to time some of the 
zinc sulphate solution must be withdrawn and its place supplied 
by water. This dilution with water and the occasional addition 
of copper sulphate, called in the telegrapher's vernacular "blue- 
stone," should be all the attention the battery requires. If left 
much on op^n circuit, additional attention is called for — the occa- 
sional scraping of the zincs to free them from deposited copper. 

The cut. Fig. 34, shows Lockwood's construction of the gravity 



116 



ELECTRICIANS' HANDY BOOK. 



cell. A spiral wire connected to the copper plate in the hottom 
of the jar lies above the copper-sulphate crystals, and is designed 
to prevent the copper-sulphate solution rising and attacking the 
zinc. It acts by decomposing the solution. There are many 
other varieties. 

Modification of the Gravity Cell. — Thomson's battery, start- 
ing with saturated solutions of both copper sulphate and zinc 

sulphate, has the latter underlying 
the former, as it is of higher spe- 
cific gravity. The zinc is in the 
bottom, the copper near the top of 
the cell. Cardarelli in 1883 is 
credited with the same idea. Cu- 
pric chloride has been used as a 
substitute for the copper sulphate. 
On open circuit the copper is at- 





Fjq. 34.-THE Gravity Battery. 
(Lockwood's.) 



Fig. 35.— D'lNFREVTLiiE's "Waste- 
less Zincs for Gravity 
Batteries. 



tacked, reducing the cupric chloride to cuprous chloride. On 
closed circuit this reaction does not take place. Delaney in- 
closed the zinc in a paper envelope, and the copper sulphate in a 
strawboard box. The zinc is but little subject in this battery to 
local action. D'Infreville's wasteless zincs provide for the attach- 
ment of partly expended zincs to the bottom of the new one. In 
ordinary practice nearly half the zinc is wasted, as the plates 
get so corroded as to require replacing. In this system such 
plates are attached below the old one, their stem, which is slightly 
conical, being forced up into a hole in the center of the other 
zinc, as shown in the sectional diagram. Pig. 35. The half-dissolved 



PRIMARY BATTERIES. 



117 



old plates are thus used up. The cut shows a partly-expended 
one below a new one. 

Sir William Thomson's gravity battery, shown in Fig. 36, 
consists of a shallow tray on whose bottom rests a sheet of 
copper. Copper-sulphate solution covers the copper plate. Four 
wooden rods rest on the copper, and carry a g;i'ating of zinc con- 
tained in a parchment paper tray or box. The resistance, owing 
to tie large surfaces and their nearness, is low compared to the 
ordinary Daniell or gravity battery. Thomson's battery in a 




Fig. 36 —Thomson's Battery. 



measure comes between the two, as the parchment paper dia- 
phragm and the specific gravity of the copper-sulphate solution 
each play a part in preventing local action. The trays are piled 
one on top of the other. 

Caustic Alkali Batteries. — Many batteries have been based 
on the action of caustic alkali on zinc. It dissolves the metal 
much as an acid does, and brings about polarization of the nega- 
tive electrode unless some means are taken to overcome it. Black 
oxide of copper, cupric oxide, is the favorite depolarizer in this 
class of battery; so much so, that the name "oxide of copper bat- 
tery" is often applied to the class. 



118 



ELECTRICIANS' HANDY BOOK. 



Lalande and Chaperon (1881). — These inventors have done 
much to bring the caustic alkali-oxide of copper couple into 
prominence. Amalgamated zinc copper in a 30 per cent solution 
of caustic alkali with copper oxide as depolarizer is the combina- 
tion. The alkali acts on the zinc, and the nascent hydrogen re- 
duces the copper oxide to the metallic form. The electromotive 
force may be as high as 0.98 volt. With electrodes 4 inches 
square and 2 inches apart, the resistance is 0.25 ohm. In one 
form an iron battery jar is used, which forms the negative elec- 
trode, taking the place of copper. As soon as a portion of the 
oxide of copper becomes reduced, the latter may operate as a cop- 
per electrode to some extent. 

In one form. Fig. 37, the battery jar and negative electrode are 




Pig. 37.— LAiiANDE's Trough Battery. 



represented by an iron tray, A. A layer of oxide of copper, B, 
is spread over its bottom. Insulating blocks, L, carry an amal- 
gamated zinc plate, D, which rests horizontally upon them. The 
caustic alkali used as excitant is covered with a layer of heavy 
petroleum oil, to prevent the carbon dioxide of the atmosphere 
from acting on the caustic alkali and destroying it. M and C are 
the binding posts. 

The Lalande and Chaperon battery does not suffer by standing 
on open circuit, as there is no local action. The chemical re- 
actions are as follows: 

Zn -{- 2K0H = Zn (KO) , + H. 

2H + Cu O = H, O + Cu. 



PRIMARY BATTERIES. , 119 

This cell can be treated as an accumulator. By passing a re- 
verse current through it, the elements are restored to their origi- 
nal state, except that the zinc electrolyzed is of such spongy con- 
sistency that it can only be used by amalgamation with a suffi- 
cient quantity of mercury. 

Modifications of the Lalande and Cliaperon Battery. — The 
Edison-Lalande battery has been quite extensively introduced. It 
is distinguished from the original Lalande and Chaperon battery 
by the use of consolidated plates of copper oxide instead of the 
granular substance. The oxide is mixed with 5 to 10 per cent of 
magnesium chloride, molded, and ignited to red heat. In this 
way a hard cake or agglomerate results. The ordinary type of 
cylindrical battery jar is used; the plates are vertical. The cop- 
per-oxide plates are held in a brass frame, which forms the nega- 
tive electrode. As the copper oxide becomes reduced on the 
surface, it may be regarded as forming a part of the negative 
plate. Caustic soda is used as the alkali. Heavy petroleum oil 
is kept on the surface of the solution, to exclude the air. The 
electromotive force is about 0.7 volt, and the internal resistance 
is 0.03 ohm. The low resistance is a good feature, compensating 
in some measure for the low voltage, which falls still lower on 
open-circuit work. A 214-pound plate of oxide of copper charges 
a 300-ampere-hour cell, or about 1/5 horse-power hour. 

Ammonium=ChIoride Batteries.— For open-circuit work zinc- 
carbon ammonium chloride batteries have had considerable 
vogue. Depolarizing is requisite unless the surface of the carbon 
electrodes is very large compared to that of the zinc. The fol- 
lowing are typical cells of this type: 

Leclanche Battery (1868). — There are two types of Leclanche 
battery, one the porous cup cell, the other the agglomerate cell. 
In the first, shown in Figs. 38 and 39, the zinc is in the outer 
vessel in a solution of ammonium chloride, the carbon is in a 
porous jar which is filled with a mixture of pulverized carbon 
and black oxide of manganese, preferably needle-form or crystal- 
line. The porous cup should be of good quality and porous. The 
electromotive force is 1.48 volts. The top of the porous cup is 
now generally sealed with pitch or some equivalent. The porous 
cup does not usually last more than two years. One part of zinc 



120 



ELECTRICIANS' HANDY BOOK. 



dissolved should reduce two parts of manganese dioxide and 
should exhaust one part of ammonium chloride. Strong ammon- 
ium chloride is advisable as it is a better solvent for the zinc 
oxychlorides formed. In the agglomerate battery there is no 
porous cup but the depolarizer is in two cakes which are held 
against the carbon plate by rubber bands. The cakes consist 
of 40 parts binoxide of manganese, 52 parts of carbon, 5 of gum 
lac, and 3 of potassium bisulphate, compressed at a pressure of 





Fig. 



.-LrciiVxcHE Battery. 



Fig. 39.— Elements of a 
Leclanche Battery. 



300 atmospheres at the temperature of boiling water. It is im- 
portant to use ammonium chloride of good quality, as the impuri- 
ties liable to occur in commercial sal-ammoniac tend to increase 
the resistance. The reaction is expressed thus: 

2NH,C1 + 2Mn02 + Zn = ZnCL + 2NH3 + H,0 + MnA- 

But there are other reactions which may occur. Thus, am- 
monium nitrate may be formed; at the beginning of the reaction 
a mixture of hydrogen and carbon dioxide and nitrogen is liber- 
ated; after a long period of action, hydrogen alone is liberated. 

Various modifications have been devised. In the Barbier cell 



PRIMARY BATTERIES. 121 

the agglomerate is molded into a hollow cylinder within which 
the zinc rod is placed. In another a cylindrical plate of zinc 
surrounds the agglomerate cylinder in addition to the interior 
rod of zinc. In these the agglomerate acts as the negative elec- 
trode; there is no carbon electrode employed. In the Gaiffe cells 
the carbon and binoxide of manganese are placed in strata or 
layers. In one form Gaiffe uses a porous cup, in the other the 
carbon is a hollow cylinder and acts as porous cup and negative 
electrode. 

The resistance of commercial Leclanche cells varies from 4 to 
10 ohms. 

Dry Batteries.— A dry battery is one which has its electrolyte 
disseminated through some solid material through which it can 
diffuse itself. Plaster of Paris and gelatinous compounds have 
been used for the solid part. The usual construction is on the 
basis of the plaster of Paris combination. 

The outer cup is made of zinc, and acts as the positive elec- 
trode. Over it is slipped a strawboard tube. The object is to pre- 
vent the zinc of two batteries from touching each other so as to 
establish a wrong connection. The negative electrode is a plate 
of carbon. This is placed in the center of the zinc, and is so 
supported as not to touch it in any place. Carbon and zinc both 
carry binding posts. The filling varies. The following is used 
in the Burnley cell: 

A wooden plunger or template, somewhat larger than the 
carbon, is inserted, and the following mixture introduced: Am- 
monium chloride, zinc chloride, 1 part of each, plaster of Paris, 
3 parts, flour 0.87 part, water 2 parts. After this has set a little, 
the wooden template is withdrawn, the carbon is inserted in the 
cavity left by its withdrawal, and the space left unfilled is filled 
with the following mixture: Ammonium chloride, zinc chloride, 
manganese binoxide, granulated carbon, fiour, 1 part of each, 
plaster 3 parts, water 2 parts. The electromotive force of this 
cell is 1.4 volts, its resistance 0.3 ohm. 

The Gassner dry cell has as negative a cylinder made of a 
mixture of carbon and manganese dioxide. The filling composi- 
tion is as follows: Zinc oxide, ammonium chloride, and zinc 
chloride, 1 part each, plaster of Paris 3 parts, water 2 parts. 



122 ELECTRICIANS' HANDY BOOK. 

For the Meserole dry battery, there are mixed the following: 
Graphite, slaked lime, arsenious acid, and glucose or dextrine, 1 
part each, carhon and manganese binoxide, 3 parts each. The 
mixture is finely pulverized and rubbed up in a saturated solu- 
tion of ammonium chloride and sodium chloride (common salt) 
with one-tenth its volume of a solution of mercuric chloride and 
an equal volume of hydrochloric acid. These constituents are 
intimately mixed and poured into the zinc cup. 

Dry batteries are sealed with pitch. A hole is sometimes left 
for the escape of gas. 

Arrangements of Batteries. — Primary batteries may be ar- 
ranged in series, in parallel, or in series multiple or multiple 
series. The best arrangement from the point of view of economy 
is to keep down the resistance of the battery by putting as 
many in parallel as is consistent with the voltage required. Each 
cell is taken as of a certain voltage and resistance. Although 
these factors change considerably, yet some basis must be taken 
for calculation, and only an approximation is attainable in prac- 
tice. 

Assume a battery of twelve cells arranged in series, and 
assume that each one has a resistance of 2 ohms and an electro- 
niotive force of 1.5 volts. The resistance of the external circuit 
is 25 ohms. What current would be produced? The total electro- 
motive force of the battery is 12 X 1.5 = 18 volts. The resistance 
of the battery, 24 ohms, added to that of the outer circuit, 25, is 

■pi -to 

24 + 25 = 49. By Ohm's law the current = :^ ^ _? ^ 0.37 

K 49 
ampere. 

Assuming the same battery arranged in parallel on the same 
external circuit. What current would be produced? The electro- 
motive force of two, twelve, or any other number of cells in 
parallel is equal to that of a single cell. The resistance of the 
battery is found by dividing the resistance of one cell by the 
number in parallel. The electromotive force of the battery, there- 
fore, is that of a single cell, or 1.5 volts; the resistance is the 
quotient of a single cell's resistance divided by the number of 

cells or A — i ohm. The total resistance of the circuit is 
13 ~ 6 



PRIMARY BATTERIES. 



123 



151 



25 + 1/6 s= 25 1/6 or •'"^ ohms 
6 

or 3/2 volt. The current by Ohm's law is 



The electromotive force is 1.5 
3 151 18 



2 • 6 ~ 302 
0.06 ampere nearly. 

Thus one arrangement of the same battery gives over six 
times the current given by the other. 

Assume that the same battery is connected on a circuit of 1/5 
ohm. With the cells in series we have an electromotive force of 
18 volts, an internal resistance of 24 ohms, an external resistance 

121 



of 1/5 ohm, a total resistance of 24 1/5 or 



ohms and a cur- 



121 



90 



rent of 18 ~ -Z^— or 0.75 ampere 



5 12L 

Assume now that the battery is connected in parallel. 



The 



Y Y k N ^1 T" 

=<)=> ^=0=' ^=0= ^=0=^ h=o= ^=0= 



U 



TTTTTT 



Fig. 40.— Battery Connected in PaballeIi or Multiple Arc. 



internal resistance is 1/6 ohm, the total resistance is 1/5 + 1/6 = 
The electromotive force is 1.5 or 3/2 volt; the current is 



y ohm 
30 



£ ^ li - ?5 = 4.09 amperes. 
2 • 30~22 
A low external resistance increases the current. An internal 

resistance equal to the external resistance gives the greatest cur- 
rent which the battery can produce through such external resist- 
ance. These are the principal laws of battery connection. 

Batteries may be arranged in other ways. Assume the battery 
to be arranged three in parallel and four in series. Its resistance 
varying directly with the cells in series and inversely with t^& 



124 



ELECTRICIANS' HANDY BOOK. 



cells in parallel, the resistance of the combination is given by 
multiplying the resistance of a single cell by 4/3; 2 X 4/3 = 8/3 
ohms, the resistance of the battery thus arranged. 

The electromotive force is unaffected by the number of cells 
in parallel but varies directly with the number in series. The 





Fig. 41.— Battery Arranged 

Three in Series and 

Two IN Parallel, 



Fig. 42.— Battery Arranged 

Two IN Series and Three 

in Parallel. 



electromotive force is therefore equal to 3 X 1.5 = 4.5 or 9/2 

volts; and the current by Ohm's law is _ _i_ — — ^ _ 1.69 

a • 3 16 
amperes. 

In late years, as primary batteries are being supplanted by 
other generators, battery calculations are of less importance than 
formerly. They should be understood and practised as they 
give an excellent insight into Ohm's law. 

In Figs. 40, 41 and 42 three different arrangements of six bat- 
tery cells are shown. 



CHAPTER VII. 

STORAGE BATTERIES. 

The Primary Battery. — A primary battery, as has been ex- 
plained, consists essentially of two plates or electrodes and of 
an electrolyte or fluid, which attacks one of the plates. As hydro- 
gen gas accumulates on the unattacked plate, some highly-oxi- 
dized substance is often used to provide oxygen. This oxygen 
combines with the hydrogen and forms water. 

Only one plate is attacked, because the material of the plates 
differs. One is made of a metal soluble In or attacked by the 
electrolyte; the other is of a material on which the electrolyte 
has no action. 

When a primary battery produces a current, three things hap- 
pen. The soluble plate, practically always zinc, dissolves. The 
electrolyte becomes exhausted as it dissolves the zinc. The de- 
polarizer becomes exhausted by giving up its oxygen to the 
hydrogen and forming water. To put the battery into working 
order, a new zinc plate, new electrolyte, and new depolarizer 
must be supplied, and the old exhausted solutions and depolar- 
izer are thrown away. This involves a great deal of labor, which 
is expensive, and requires new zinc and chemicals, which are 
also expensive. 

Action of a Storage Battery.— A typical storage battery in- 
cludes the elements cited above. There is an electrolyte, two 
plates, and a depolarizer. The production of current oxidizes 
and may dissolve the material of one plate, and the electrolyte 
is exhausted in the process. The hydrogen, which seeks the 
inactive plate, finds there a depolarizer, and this is gradually 
decomposed and reduced as it supplies oxygen to the hydrogen. 
After a time the battery is exhausted, and no longer in a condi- 
tion to produce current. 



126 ELECTRICIANS' HANDY BOOK. 

Regeneration. — ^To regenerate it, neither labor nor supplies are 
needed. A current of electricity of opposite direction to that 
which the battery originally produced is passed through it. 
This reproduces by electrolytic reduction the attacked electrode 
on one plate; it forms upon the other plate the depolarizer, 
also by electrolysis. As these two actions take place, the elec- 
trolyte is restored to its original strength. After a sufficient 
time of "charging," as this process is termed, the battery is 
restored to its original condition. The charging current is 
stopped, and the battery is ready for producing current again. 

In place of labor, chemicals, and new zinc plates we have elec- 
tric energy, in the shape of a current with electromotive force. 
The electric energy is produced at a cost far less ttian the equi- 
valent in primary battery supplies. The storage battery also 
has an exceedingly low resistance. These are the causes of 
its economy, and its economy has made it available for the 
heaviest service. 

The accumulator, storage battery, or secondary battery as it 
is indifferently called, is a battery which, when polarized or ren- 
dered inactive by production of a current for a time, can be re- 
stored to its original condition by passing a current through it 
in the reverse direction. 

Grove's Gas Battery. — Grove's gas battery, which dates back 
to 1829, is the first prominent storage battery. Plates of plati- 
num are contained in tubes airtight at the top and open at 
the bottom. The lower ends are immersed in vessels of dilute 
sulphuric acid, each tube being filled with acid before immer- 
sion, and kept full until immersion. Air pressure then main- 
tains the column of water in each tube. The platinum plates are 
connected as shown in the cut. Fig. 43. MM are the cups of 
dilute acid. P and N indicate the main leads. A charging cur- 
rent entering at A and leaving at B charges the tubes A, A', etc., 
with oxygen gas, and those marked B, B', etc., with hydrogen 
gas, H. The latter has almost exactly double the volume of the 
oxygen, O, as is indicated by the level of the letters H and O in 
the cut. By this operation the platinum plates are caused to 
emerge from the solution. When pretty well exposed, each sur- 
rounded by its own gas, oxygen and hydrogen respectively, if 



STORAGE BATTERIES. 



127 



the terminals are disconnected from the charging circuit, a cur- 
rent in the reverse direction can be talven from the battery by- 
connecting the plates with a wire just as if they were ordinary 
battery plates. The hydrogen and oxygen disappear as current 
is taken, and the plates become covered with the solution again. 
The platinum plate in the oxygen tube represents the copper or 
carbon plate in an ordinary battery. The hydrogen in the other 
tube represents the zinc. The platinum plate plays the role of 
conducting electrode. 




Fig. 43.— Grove's Gas Battery. 



Sometimes the battery was charged by introducing hydrogen 
and oxygen gases directly into the tubes. 

Under favorable circumstances each couple gives 0.843 volt 
electromotive force. 

Even before Grove's date, in 1803, Ritter built up piles with 
disks of identical metal throughout separated by cloth mois- 
tened with dilute sulphuric acid. A current passed through this, 
caused hydrogen gas to accumulate on one face of the disks and 
oxygen on the other. On disconnecting it from the source of. 
current, a reverse current was given by it when its terminals 
were connected. 



128 ELECTRICIANS' HANDY BOOK. 

Much work of scientific interest has been done in this line 
of research. Palladium and carbon have each been substituted 
for platinum, and the effect of a porous diaphragm separating 
the plates has been tried. 

The gas batteries are only of scientific interest, they have no 
practical value. The following have been given as the require- 
ments of a practical storage battery. 

Requirements of a Storage Battery.— It must absorb the great- 
est quantity of "electric energy" with the smallest volume, and 
above all with the smallest weight. The charge should be re- 
tained for long periods without loss. The battery should make 
a good return; its efficiency should be high. The battery should 
give a constant current, without intermittence, and should be 
subject to regulation. 

Function. — Before going on with the subject, the function of 
storage batteries may again be referred to. They do not directly 
store electricity, except a little which is incidental only and 
not taken into account. Their action is simply to provide a 
battery which when exhausted can be brought back into its orig- 
inal condition by electrolysis. It is as if a carbon zinc sulphuric 
acid couple were so constructed that when the acid was expended 
and the zinc dissolved, we could rejuvenate the cell or repro- 
duce zinc and electrolyte by passing a current of electricity 
through the battery. The current would have to go in the oppo- 
site direction to the natural current of the battery. 

As a matter of convenience, we speak of the amount of elec- 
trical energy a battery can store up. Properly, it is potential 
chemical energy which is stored up; the other expression is 
practically correct, and can be used to express the result. As 
long as the action of the battery is understood, the convenient 
expression can be used without implying a misunderstanding of 
the th-eory. 

Plant6*s Battery.— In 1859 or 1860 Gaston Plante first solved 
the problem. The importance of his work is shown by the use 
of the Plante principle in batteries of the present day. Lead- 
plate electrodes are still the most successful ones for storage 
batteries, and to Plante is credited their first use in this role. 

His original battery was made of two sheets of lead. They 



STORAGE BATTERIES. 



129 



are laid flat, one above the other, with a non-conducting sub- 
stance or strips between them. Canvas was one of the first 
separators used; later, India-rubber strips were employed. The 
plates have each a strip of its own substance projecting from 
a corner. The two plates with intervening insulating strips or 
equivalent are then rolled up into a spiral. The process and 
its result are shown in Fig. 44. The plates must not touch, or 
the couple will be short-circuited and inactive. The plates are 
immersed in a 10 per cent solution of sulphuric acid. 
Forming.— The next process is the forming of the plates. The 




Fig. 44.— Plante's Storage Battery Plates. 



object is to cover one plate with as thick a coating of lead per- 
oxide as possible, and to make the surface of the other plate as 
spongy as possible. The new battery is first subjected to the 
forming process. One lead plate is connected to one terminal 
of a circuit and the other to the other. One plate of lead col- 
lects oxygen and is oxidized. The other evolves hydrogen gas. 
After this is kept up for a while, the charging circuit is re- 
moved and the plates are connected by a wire. A current in 
the opposite direction to that of the charging current is now 
produced. When no more current is generated, the charging 
circuit is reconnected, but in the reverse of the former direction. 
The process goes on as before, except that this time the other 
plate is oxidized. Then the battery is discharged, and is re- 



130 



ELECTRICIANS' HANDY BOOK. 



charged in the original direction. This sequence of processes 
may be kept up several months. It is of importance, before 
connecting the reversed charging current, to have the battery 
almost completely discharged. Sometimes the solution is heated, 
to accelerate the forming process. 

To assist the forming process, the surface of the plates may 
be mechanically roughened, or may be corroded with dilute 
nitric acid. When formed, one plate is 
reddish in color because it is covered with 
binoxide of lead, PbOa. This plate is called 
the positive plate in storage battery nomen- 
clature, although it corresponds to the car- 
bon plate in primary batteries. Many modi- 
fications of the battery have been made. 

The first electromotive force given by a 
Plante couple is 2.53 volts. This soon falls 
to 2.1 volts, and for two-thirds of the dis- 
charge it remains at 2.02 volts. 

The resistance of a cell with 775 square 
inches of total lead surface with plates 0.2 
inch apart varies from 0.04 to 0.06 ohm, ac- 
cording to the condition of the plates. 

Storage Capacity. — A Plante couple will 
give 36,300 coulombs per kilogramme of 
lead for its whole discharge. At 2 volts 
Fig. 45.— Fahbe's Stor- *^^^ gives 72,720 volt-coulombs, or about 
AGE Battery. 95 horse-power seconds, or about 0.03 horse- 

power-hour of energy. It returns 89 to 90 
per cent of the coulombs used in charging it. As much as 19 
grammes of copper per 1,000 grammes of lead electrodes has been 
deposited by it on a single charge. 

By connecting 800 elements in series, M. Plante obtained sparks 
2 inches long. 

Faure's Battery.— In 1881 Faure used red oxide of lead in 
combination with lead plates. The plates were coated with a 
paste of red lead and acid. Parchment paper and felt were placed 
over the layer, and the plates were rolled up with intervening 
strips of India rubber, as in Plante's original cell. It is shown 




STORAGE BATTERIES. 131 

in Fig. 45. This construction was defective from, several aspects. 
The felt increased the resistance, might tear and short-circuit 
the plates, and the lead oxide had very poor adherence. 

The Faure=Senon=Volckmar Battery. — In this battery the 
felt and parchment paper were not used. The plates were 
pierced with holes, and red lead was packed into the holes in the 
positive plate and litharge into those in the negative plate. In 
charging, the litharge is reduced to spongy lead, the red lead is 
oxidized to brown oxide (PbOo). 

In this battery straight plates or grids were substituted for 
the spiral rolled plates of the Plante and Faure cells. The 
weight of a 30-kilogramme cell (66 pounds) was thus divided: 

Lead electrodes and oxides 16.8 kilos. 37 pounds 

Acid 6.5 kilos. 14 pounds 

Cell 6.0 kilos. 13 pounds 

29.3 kilos. 64 pounds 
The formation of the cell took about 100 hours. An electro- 
motive force of about 2 volts was produced on its discharge. 

Chemical Action. — The following reactions are ascribed to the 
storage cell with lead plates, by Gladstone and Tribe. First is 
the discharge or action of the battery: 

- + - + 

Pb + 2H2 SO4 + Pb 0, = Pb SO, + 2H2O + Pb SO,. 
The — and + signs above the line indicate the positive and 
negative electrodes. For the charge the layers of lead sulphate, 
Pb SO,, have to be brought back to their original condition, one to 
metallic lead, Pb, the other to peroxide of Pb Oo. 

+ 
+ Electrode Pb SO, + O + H,0 = Pb O., + H, SO,. 

— Electrode Pb SO, + 2H = Pb + H, SO,. 

There are other theories. The above is so simple that it 
will answer in the existing circumstances as at least a general 
explanation of the reactions. 

A great number of variations in construction of storage bat- 
teries have been tried. It is astonishing how small a departure 
from the Plante and Faure-Sellon-Volckmar cells has been made 



132 ELECTRICIANS' HANDY BOOK. 

by modern constructors. The Plante plate slightly modified, is 
still in use in modern batteries. But Plante did much more than 
is spoken of here. He constructed batteries with flat parallel 
plates separated by insulating buttons, not confining himself to 
spiral plates as in his first efforts. 

Resistance. — The increasing of the plate area in storage bat- 
teries effected an improvement in the direction of efficiency of 
the entire circuit. It lowered the resistance. The nature of 
the electrolyte in Plante's battery added to this effect, as the 
conductivity of dilute sulphuric acid is high. All storage bat- 
teries are constructed with a view of lowering resistance, and 
for industrial purposes are made very large. The effect of this 
is that exceedingly large currents can be taken from them. 

To accelerate the charging process, or to give the plates a 
better and deeper active area, subdivision of the plate surface is 
resorted to. 

Gould Storage Battery. — In this battery the Plante system of 
direct formation of a solid lead plate is adhered to, but to in- 
crease the surface the lead plate is mechanically treated. 

A very dense rolled lead of chemical purity is used for the 
plates. This is cut into blanks of the desired size of the plate. 
The blanks are placed in steel frames, and caused to move 
back and forth in reciprocating motion between two rollers. 
These rollers consist of revolving shafts on which are strung 
steel disks, separated from one another by alternate washers, also 
strung on the shaft. The composite rollers press upon both 
surfaces of the lead, and form it into ridges and grooves. The 
shape and spacing of the steel disks determine the shape of 
ridges and grooves. 

The action is not simply cutting. The lead yields to the- 
pressure, and by "cold flowing" rises up into ridges between the 
forming disks. No lead is removed, it is simply pressed, burn- 
ished, and spun into shape. The length of path traversed by 
the rollers can be varied. On the small plates it is a little short 
of the length of the plate. This leaves an unspun portion at 
each end, which portion anchors the ribs in place. On large 
plates, by rolling the plate in two or more sections, a number 
of transverse unspun portions are left, and sometimes vertical 



STORAGE BATTERIES. 



133 



strengthening bars are left untreated. A plate may be divided 
thus into any desired number of areas of ribbed surface, sepa- 
rated by solid bars or bridges to stiffen the plate and anchor the 
ribs. 

This process increases the surface of the lead from ten to 
twenty fold, yet gives a one-piece plate. From 200 to 400 square 
inches of surface per pound of lead are produced; 250 square 
inches of surface per ampere of normal current is given. The 
ribs vary from 0.005 to 0.040 inch thick, according to the work 
they have to perform. The negative plate generally has ribs 
0.012 inch thick. The grooves vary from 0.005 to 0.024 inch wide. 



^ 



NEGATIVE 





"^^ 


3 




ss^« 


._.=. 


ii^-—^--;— ■ 


~ 


:::.==..-^ 



y? 



Fig. 46.— Positive and Negative Plates of Gould's Storage Battery. 



When the plates are formed, which is done electro-chemically, 
the grooves become charged with material, lead peroxide or re- 
duced lead, whose presence reinforces the ribs. 

The great area of active surface operates to give the battery a 
very low resistance, so that a very heavy current can be taken 
from it. 

In the cut, Pig. 46, a positive and negative Gould plate are 
shown. 

HeHos=Uptoii Battery, Philadelphia.— The plates in this bat- 
tery are made of chemically-pure lead. They are sawed trans- 
versely part through, so as to form them into narrow horizontal 
grooves very close together. They are formed by electro-chemi- 
cal process. The positive and negative plates for each cell, con- 



134 



ELECTRICIANS' HANDY BOOK. 



stituting an element, are insulated or kept apart by rubber sep- 
arators, and are bound together, so as to form a unit, which 
can be readily handled and lifted about by grasping both 
end bars at once. The manufacturers prescribe as a minimum 
discharge limit 1.5 volt, which is lower than that normally 
allowed in general practice. Portable batteries are shipped ready 
for use with electrolyte in the cell. An efficiency of 93 per cent 
and a current of 5 amperes per pound of element in continuous 
commercial operation is claimed for it. A two-year guarantee is 




Fig. 47.— Front Yirw and Cross-section of PiiATa of American 
Storage Battery with Separator, 



given, provided the battery is charged and discharged at normal 
ratings. 

American Storage Battery.— The storarge battery made by 
the American Battery Company, of Chicago, is illustrated in 
one of its distinctive varieties in the cuts. The lead plates are 
horizontally grooved as shown, with the grooves looking upward. 
This construction prevents material dropping from them to the 
bottom of the cell. Insulating strips are placed between the 
plates. The strips are notched at the ends, and three are placed 
between each two plates. India-rubber bands are sprung around 
the plates, passing through the grooves on the ends of the in-- 
sulating strips. The bundle of plates can be taken in and out 



STORAGE BATTERIES. 



135 



of ttie cells without danger of injuring the plates in any way. 
The plates are made of pure lead, and are electro-chemically 
formed. The battery is designed to be very substantial. 

The cut. Fig. 47, shows on the left the front view of a plate 
whose cross section is shown in the center figure. On the left 
is a separator. The next cut. Fig. 48, shows the element com- 
plete, with the separators in place and all bound firmly together 
by bands of insulating material. 
India rubber is the material used. 

Crompton=>Howeil Battery. — In 
this battery of English manu- 
facture, a porous or honeycombed 
lead plate is used. Such plates 
may be made by mixing with lead 
a quantity of fragments of metal 
attacked by sulphuric acid. Iron 
turnings might thus be used. The 
lead melted and mixed with iron 
borings would then be cast in 
molds. On treatment with acid 
the iron would dissolve and leave 
the lead full of small openings. 
The plates made on these lines 
are formed by the charge and dis- 
charge method. One size of plate 
is 9 X 9 inches and i/4 inch thick. 
A cell with 61 plates maintains a 

1,000-ampere current for 30 minutes before the potential falls 
much below the normal. 

Pasted Plates. — The use of oxide of lead mixed with sul- 
phuric acid to a paste, and held on the smooth surface of a lead 
plate by parchment or other attachment, proved a failure in the 
Faure battery. Pasted plates, as they are called, are made with 
perforations or equivalents in the lead plates, for the purpose of 
retaining the oxide. Apertures may be dovetailed in cross-sec- 
tion, so as to retain more firmly the lead oxide which is pressed 
into them. 

E. P. S. Battery. — This is an English battery made by the 




Fig. 48.— Set of Elements of 

AN American Storage 

Battery Cell. 



136 



ELECTRICIANS' HANDY BOOK, 



Electric Power Storage Company, the initials of whose title give 
it its designation. One of its varieties is shown in the cut. Fig. 
49. The plates or grids are cast full of holes, smaller in the 
center than on the two surfaces, so that the section of the hole 
represents two dovetails put together. The holes in the positive 
plate are filled with a mixture of red lead, Pbs O^, and dilute 

sulphuric acid. This ox- 
ide is the next to binox- 
ide, PbOo. The latter is 
the characteristic oxide 
of the positive plate. The 
holes in the negative plate 
are filled with litharge, 
PbO, made into a paste 
with sulphuric acid or 
with solution of magne- 
sium sulphate. 

The forming seems like 
an intensive process when 
contrasted with the slow 
Plante forming. A strong 
current of 48 hours' dura- 
tion forms the positive 
plate, and half the dura- 
tion serves for the nega- 
tive plate. The plates are 
soaked in dilute sulphuric 
acid before forming. 
When set up in the cells 
they are separated by 
glass rods. The plates have downwardly-extending prolonga- 
tions forming feet on which they rest on strips of wood or equi- 
valent in the bottom of the cell. 

Chloride Battery. — This battery is made by the Electric Stor- 
age Battery Company, of Philadelphia. Lead is melted and 
blown into a fine spray, which cools and falls in fine shot. It is 
dissolved in nitric acid, and precipitated as lead chloride, Pb CI2. 
The lead chloride is melted, after drying, with zinc chloride, 




Fig. 49.— E. P. S. Storage Battery ; L Type. 



STORAGE BATTERIES. 137 

and is cast into tablets. These are % inch square and from 14 
to 5-16 inch thiclv. They are supposed to coincide in thickness 
with the plates. The tablets are arranged in a mold 0.2 inch 
apart, and held there by pins. Lead is melted and forced in 
under a pressure of 75 pounds to the square inch. 

The metallic lead solidifies as it cools, and holds the tablets 
of lead chloride firmly in position. When cool, the plates rep- 
resent lead grids or gratings with the openings filled with the 
solid mixture of lead chloride and zinc chloride. The plates are 
now placed in a tank alternating with zinc plates, the plates be- 
ing in contact with each other. A solution of zinc chloride, 
Zn CI2, is contained in the tanks. Galvanic action is set up; the 
metallic zinc is attacked, hydrogen goes to the lead plates and 
reduces the lead chloride to metallic lead. The hydrogen com- 
bines with the chlorine of the lead chloride and forms hydro- 
chloric acid, so that the lead chloride is a depolarizer for this 
action. The zinc chloride dissolves. 

Thus there is eventually produced a lead grid whose openings 
are filled with spongy lead. A thorough washing removes all 
soluble salts, and the plates are now ready for forming. The 
great area of surface due to the spongy lead, and its firm reten- 
tion in the openings, favor the production of a plate deeply at- 
tacked in use and yet strong and durable, which are desirable 
features. This type of plate is especially adapted for the posi- 
tive plate, as the spongy lead is in an excellent condition for 
oxidation and formation of lead binoxide. 

The action on the plugs of mixed chlorides is two-fold. The 
lead chloride is reduced by the galvanic action to the metallic 
state, and the zinc chloride dissolves out. The object of the 
zinc chloride is to supply the element of porosity. As it dis- 
solves it exposes the lead chloride in the interior of the tablets 
to galvanic action, so that it is reduced. The plates, when the 
tablets are reduced, are formed by the regular process. 

Constant efforts are made to improve the storage battery, 
either as regards cost or efllciency. As a negative plate the fol- 
lowing construction has been tried. A lead grid has its openings 
filled with litharge made into a paste with sulphuric acid. Over 
each face of the grid a perforated plate of lead is soldered. This 



138 



ELECTRICIANS' HANDY BOOK. 



operates to pocket the litharge. In forming the litharge is 
reduced to metallic lead of the spongy type with large active 
area. The perforations in the inclosing lead plates give the 
electrolyte free access to it. An antimony alloy, lead 95 per 
cent, antimony 5 per cent or thereabouts, has been used for the 
positive plate, with circular holes in it, 25/32 inch in diameter, 

set diagonally to each other. 
Corrugated lead ribbons 7/16 
inch wide, which is the thick- 
ness of the plate, are rolled into 
close spirals and are forced into 
the apertures in the plates. A 
current of 30 hours' duration is 
required to form these plates. 

In the batt-ery cell the plates 
are separated by cherry wood 
partitions, or glass rods are used 
as in the English E. P. S. cell. 
Grooves running vertically are 
made on the surface of the 
plates, to facilitate the escape 
of hydrog-en and oxygen gas in 
the charging process. 

Tudor Battery, — The charac- 
teristic of this battery is the 
treatment by charging or form- 
ing process of the plates as a 
preliminary operation before ap- 
plying lead-oxide paste. The 
plates are groov-ed transversely 
with grooves of semicircular cross section. After the plates have 
had lead binoxide, Pb O., formed upon them, they are pasted with 
lead oxides in the regular way, and are then rolled. 

Sometimes two types of plates are used in one battery. The 

Plante type is very available for positive plates. The Tudor type 

is sometimes used for this service with chloride type negatives. 

Suspended Plates .—The cut, Fig. 50, shows how the plates of 

one of the batteries of this company are suspended in the cell. 




Fig. 50.— E. S. B. Stobaqe Battery 
WITH Elements Carried on 
Walls or Trough. 



STORAGE BATTERIES. 



139 



Projections from the shoulders of the plates rest on the upper 
edge of the cell. In Figs. 51 and 52 another system used by 
the same company is shown. Two heav<y plates of glass rest in 
a vertical position on supports in the bottom of the cell, and 
on these the plates rest. These cuts also show the use of glass 
supports or insulating feet for the cell, and the connection of 
the plates by bus-bars of lead. 

Other Types of Pasted Plates. — It is impossible to give any- 





FiG. 51.— Storage Battery with 
Bus-Bars, and Elements Car- 
ried on Glass Plates. 



Fig. 53.— Interior of Storage 

Battery with Bus-Bars and 

Elements Carried on 

Glass Plates. 



thing approaching a complete presentation of the many variations 
of pasted and compound plates. As an example of other meth- 
ods of making such plates. Figs. 53 and 54 are given. Fig. 53 
shows a section of a plate with apertures adapted to retain the 
paste introduced. The edges of the openings were burnished or 
rolled down after the paste was introduced, thus binding it in 
place. Fig. 54 shows a plate made by casting lead around little 
cylinders of porous lead oxide made up beforehand. 

Copper Storage Batteries.— In this type of battery the posi- 
tive plate is peroxidized lead, as in the lead-plate batteries; the 



140 



ELECTRICIANS' HANDY BOOK. 



negative is copper-plated lead. The liquid is an acid solution of 
copper sulphate. The electromotive force of a cell is 1.68 volts. 
In another form amalgamated lead was used. The mercury dis- 
solved during the charging process, and left the lead in a better 




Fig. 53.— Section of Drake & Gorham's Storage Battery Plate. 



condition for peroxidizing. An advantage claimed for copper 
sulphate storage batteries was that the color of the solutions 
showed their condition. When it was colorless, they were fully 
charged; when discharged, the solution was blue. 

Zinc Acid Storage Batteries. ^In this 
type the positive plate is peroxidized lead; 
the negative is zinc-plated lead, the solu- 
tion is an acid solution of zinc sulphate. 
The electromotive force is 2.3 volts. 

WaddeU=Entz Battery.— This is a cop- 
per oxide zinc caustic potash couple. Some 
years ago it was used on one of the street ' 
railroads in New York, but never acquired 
very extensive use. The operation of dis- 
charging is that of the Lalande-Chaperon 
battery. Oxide of copper, CuO, coating 
the positive plate, is reduced to metallic 
copper, and zinc is dissolved from the 
negative plate. On charging, the positive 
plate is oxidized to copper oxide. The 
alkaline solution of zinc is electrolyzed, 
and metallic zinc is plated or deposited 
Like the Lalande-Chaperon cell its elec- 
being only 0.7 volt; about one-third that 




Fio. 54.— Reckenzaun's 

Storage Battery 

Plate. 



on the negative plate, 
tromotive force is low, 
of the ordinary Plante type of battery. 

Edison's Storage Battery. — This battery was originally de- 



STORAGE BATTERIES, 141 

signed to meet the requirements involved in operating an elec- 
tric automobile. • The service is a very severe one, and greatly 
reduces the efficiency of the lead plate battery, because the cur- 
rent is sometimes used at such high rates. The lead plates are 
liable to suffer greatly at these high discharge rates and in the 
mechanical disturbance to which they are subjected. The wear 
on the battery is excessive. The lead plates are exceedingly 
heavy, which is a disadvantage. 

In designing a battery to compete with the lead plate com- 
bination, no comparison can be instituted with the efficiency 
or durability of the carefully treated station battery. In an elec- 
tric power station, charge and discharge are exactly regulated, 
and every precaution is taken to maintain the battery in the 
best condition of efficiency. In an automobile the discharge 
rate on hills has to be very heavy. The automobile is supposed 
to take the people in it home, and to do this the discharge may 
be carried too far. 

The Edison battery, possibly of lower efficiency than the lead- 
plate battery, is almost unaffected by causes which operate dis- 
astrously on the lead-plate combination. It can be charged and 
discharged at high rates without hurting it. The ability to stand 
rapid charging may be of considerable advantage in the condi- 
tions confronting its use. 

A steel grid 1/40 inch thick is the foundation for a plate. It 
contains in the one illustrated. Fig. 55, twenty-four perforations. 
For each perforation there is provided a little perforated steel 
box or pocket. Each pocket is made in two pieces, one entering 
into the other, like the top and bottom of a very shallow tin 
box. Each box is 3 inches long, % inch wide, and 3/16 inch 
deep, fitting the perforations accurately. 

Two sets of briquettes or cakes are made, which go into the 
boxes, one set for the positive plates containing oxide of nickel; 
the other set for the negative plate containing oxide of iron. 
Graphite is mixed wath the oxides to improve the conductivity. 

If a positive plate is being made, the twenty-four boxes ap- 
pertaining to it are filled with* the nickel-oxide briquettes, the 
perforated cover is put on each, and they are placed in the 
openings in the grid. The whole is now subjected to high 



142 



ELECTRICIANS' BANDY BOOK. 



pressure. The platen and bed of the press have ribs which, 
corrugate the boxes. They are compressed to about one-third of 
their original thickness. As they expand laterally under the 
pressure, they are driven against the sides of the holes in the 
steel grids, and their sides bulge out over the ribs of the grids 
on both sides of them. The whole combination of grid and 
twenty-four pockets is consolidated thus into a strong plate, 
free from shake, with good electrical contact between boxes and 



/"^-— — ~_ 




Fig. 55.— The Edison Grid Filled and 
Uneilled and Briquettes. 

grid. The negative plates receive identical treatment. There 
is no difference in appearance between positive and negative 
plates, the characteristic colors of positive and negative of the 
lead plates finding no representatives. 

The electrolyte is a solution of caustic soda or caustic potash. 
The solution suffers no change in use except in its gradual 
loss of water. 

The containing jar is of corrugated sheet steel, and hard-rub- 
ber supports and separators for the plates are used. The plates 



STORAGE BATTERIES. 



143 



are grouped in alternation. Fig. 56, just like the plates in a lead- 
plate storage battery, with insulating separators and supports. 
Fig. 57. 

The action of the battery is simple. The charging current oxi- 
dizes the nickel to superoxide Ni O2, and reduces the iron to the 
metallic state. In the discharge the iron is oxidized, and the 
nickel superoxide is reduced. 




Fia. 56.-^The Edi- 
son Storage Bat- 
tery Elements 
Grouped. 




Fig. 57.— The Edison Stor- 
age Battery Supporter 
AND Separators. 



The cover is soldered to the jar, and is provided with two 
.stuffing boxes, through which the terminals or pole pieces pro- 
trude. Another mounting on the top is called a separator. It 
contains wire gauze to catch any spray which may be thrown 
up in the charging. This acts to economize solution. Another 
mounting is called the filler. This is designed for the introduc- 
tion of the 20 per cent solution of caustic potash which forms 
the electrolyte, or for the addition as required of distilled water. 

It would seem difficult to add the right amount of water to 



144 ELECTRICIANS' HANDY BOOK. 

an opaque, tightly-sealed cell. A patented funnel is provided 
with the battery, which contains a water-level indicator, over- 
coming this difficulty. 

Hard-rubber insulators separate the cells, and they rest upon 
sheets of the same material of suitable shape. Four projec- 
tions on each fit into corresponding depressions in the bottoms 
of the cells. Four wooden buttons on the tray bottoms fit into 
the indentations in the India-rubber insulators beneath their pro- 
jections. These trays of specially selected and prepared wood 
hold four, five, or six cells. 

The highest voltage of discharge, immediately after charge, is 
1.5 volts. The mean voltage is 1.1 volt. The normal time for 
charging is three and one-half hours; it can without injury be 
charged in an hour. A cell with fourteen positive and fourteen 
negative plates gave 42.5 amperes for six hours. The voltage 
started at 1.45, fell to 1.3 in half an hour, slowly sank to 1 volt 
in five hours, and then in a few minutes to 0.5 volt. At the 
end of six hours the voltage was almost gone. 

Its weight is between 50 and 60 pounds per horse-power-hour. 

The Discharge. — The normal rate of discharge of lead-plate 
storage batteries is eight hours. They can be discharged at a 
much higher rate. At a high rate of discharge the ampere-hours 
are less than at the slow rate. The voltage is also somewhat re- 
duced, so that there is a large reduction in efficiency. The eight- 
hour rate has come to be regarded as a standard for all lead 
cells. If the discharge is completed in an hour by taking a very 
heavy current from the battery, only one-half the ampere-hours 
are obtained, and the efficiency is less than 50 per cent of the 
normal. 

A rapid discharge is apt to injure the plates mechanically. 
If they are composite plates of pasted type, they are especially 
apt to be injured, the "plugs" or active portions being loosened 
or disintegrated. The Plante type may be expected to resist this 
treatment better than composite plates. 

Discharge on Open Circuit.— If a battery is charged and left 
standing on open circuit, it loses nearly 4 per cent of its charge 
each day. 

rianufacturer's Data. — When a battery is supplied, the manu- 



STORAGE BATTERIES, 145 

facturer gives tlie data as regards the charging and discharging. 
The two rates are expressed in amperes, and are generally iden- 
tical. They vary with the time for the discharge, but the charge 
is usually based upon a period of eight hours. 

Determination of Discharge. — There are several ways of de- 
termining when a cell should be considered as discharged. 

The voltage should not be allowed to fall below 1.70 to 1.75 
volts. When it reaches this point, the cell should be put out of 
use and recharged. Some authorities give 1.8 volts as this 
limit. 

The specific gravity of the acid in the cell changes slightly. 
It is reduced as the cell is discharged. No absolute figure can 
be given, as the electrolyte in different installations will often 
vary. The operative must learn to know his battery. 

The manufacturer gives the discharge rate. If the discharge 
rate is multiplied by the hours, the coulombs can be calculated 
therefrom. A meter will tell the coulombs taken from the bat- 
tery. As soon as these are equal to the coulombs deduced from 
the manufacturers' figures, the battery may be taken as dis- 
charged. 

The positive plate, which when charged is darker in color, 
varying from light brown to almost black, grows lighter in tint 
as the battery is discharged. This change is a very poor cri- 
terion. No matter how much confidence an operative may have 
in his ability to judge by it of a cell's condition, color cannot be 
trusted as more than an approximate test. 

The Charge. — After a battery has been discharged, the best 
practice is to charge it immediately. The rate of charging is 
given by the manufacturer. The voltage of the dynamo must 
be sufiicient to produce this current against the electromotive 
force of the battery. As the battery receives its charge its volt- 
age rises, so the voltage of the dynamo may have to be in- 
creased, because the voltage of the battery is opposed to or coun- 
ter to that of the charging dynamo. 

The voltage required for charging at any instant will always 
be in excess of that which the battery would give at that par- 
ticular moment. The ohmic resistance of the circuit has to be 
overcome, as well as the counter electromotive force, and to over- 



146 ELECTRICIANS' HANDY BOOK. 

come the latter an excess of electromotive force is required from 
the charging dynamo. Hence there is a loss in energy involved 
in this difference of electromotive forces. 

This is sometimes not taken adequately into account in dis- 
cussing storage-battery action. The charge will be said to re- 
quire a certain number of ampere hours, and the discharge will 
be said to give a certain number. But the ratio of these quan- 
tities does not at all express the efficiency of the battery. The 
watts used in charging and those given on the discharge are 
th3 data for determining the efficiency, and these depend on 
the voltage as well as amperage. 

As the battery receives its charge, the voltage rises. The rise 
is more rapid at the beginning and end of the charge. When a 
voltage of 2.5 per cell is reached, the charge is within 90 per 
cent of the rated charge, and the operation may be considered 
complete. 

Although a normal charging rate based on eight hours' charg- 
ing is given by the makers, this can be exceeded. If a higher 
rate is used, the hours must be proportionately diminished, so 
that the product of hours by amperes will be the same in both 
cases. 

Specific Gravity Variation of Electrolyte.— After a battery 
is in working order, the specific gravity of the solution in the 
cells should be taken when it is fully charged and when it is 
discharged. These two figures, which will differ from each 
other by about 0.025, may be used to determine the condition of 
the battery subsequently. The solution in different batteries 
varies slightly, so for each one the specific gravity should be 
determined. The specific gravity of the solution when the bat- 
tery is charged should be about 1,225; when discharged, about 
1,200. 

The reason of this variation in specific gravity can be under- 
stood from the general description of the action of the lead-plate 
storage battery given on page 131. When a battery is discharged, 
a part of the sulphuric acid has combined with the lead and 
formed lead sulphate on both plates. Lead sulphate is almost 
insoluble in water and in dilute sulphuric acid. The acid com- 
bined with the lead is therefore withdrawn entirely from the 



STORAGE BATTERIES. 



147 



solution. Sulphuric acid has a much higher specific gravity 
than water, so that its removal from . the solution reduces the 
specific gravity thereof. When the battery is charged, the lead 
sulphate on both plates is decomposed, lead binoxide and me- 
tallic lead being formed from the sulphates, and the sulphuric 
acid radical enters into solution, forming sulphuric acid and in- 
creasing the specific gravity of the solution. 
The specific gravity is usually determined 
by a sensitive hydrometer. If not sensitive, 
it is useless for storage battery work. 

Hydrometers.— Fig. 58 shows two kinds 
of hydrometer. One is a tube perforated 



Fig. 58— Hydbo- 

2x£i J. £jXvO • 




Fig. 



-Hydrometer Set. 



at the bottom and containing beads of varying specific gravity, 
the heavier ones below in order of their specific gravity. A hook- 
ed tube at the top admits air. Immersed in the solution, the 
bulbs which fioat give the approximate specific gravity. The 
other is the regular floating hydrometer. It floats higher as the 
liquid is heavi-er, and the scale on its stem is to be read at the 
level of the solution. 

The floating hydrometer may be floated directly in the bat- 



148 



ELECTRICIANS' HANDY BOOK, 



tery jar. Often a heavy glass test tube, shown in Fig. 59, is 
used to hold it, and the test tube is filled by a pipette with 
India-rubber bulb. On putting the mouth of the tube in the 
solution of a jar, squeezing and releasing the bulb, the solution 




Fig. 61— Fydrometeb 
AND Pipette. 



Fig. 61.— Stationary Scale Hydrometer. 

(HolJen's.) 



is drawn up and can be dropped into the test tube by squeezing 
the bulb. Another apparatus is shown in Fig. 60. The hydro- 
meter is inclosed in a pipette. A stricture or annular projection 
at the middle of the pipette keeps the hydrometer away from 
the walls of the pipette. By placing the open lower end of the 
pipette in the solution with the bulb squeezed and releasing it, 



STORAGE BATTERIES. 149 

the solution rises into the pipette and floats the hydrometer. Fig, 
61 shows a hydrometer without graduation, a scale attached to 
the battery plate, and just touching the solution with its pointed 
lower end, giving the basis for reading. This obviates the read- 
ing of the water level on the stem of the hydrometer, which is 
rather inaccurate. 

Gassing.— When a battery is receiving its charge, the water 
in the electrolyte undergoes decomposition, hydrogen going to one 
plate and oxygen to the other. The hydrogen reduces the lead 
oxide of the lead sulphate on the negative plate to metallic lead, 
with formation of water. The oxygen oxidizes the lead oxide 
of the lead sulphate on the positive plate to lead binoxide. Sul- 
phuric acid is produced from the lead sulphate on both plates. 

If a battery worked perfectly, it is evident from the above 
that no gas should be given off. Some evolution of gas may be 
looked for always during the last hours of the charging process. 
A slight bubbling may occur during most of the charging pro- 
cess, but much of the hydrogen and oxygen are disposed of 
as described above, and do not appear as gases. But when the 
battery is charged, the sulphate on the plates is exhausted, and 
can no longer dispose of the oxygen and hydrogen. These are 
then evolved in quantity, and the battery "gases" violently. 
Sometimes the solution, which is really transparent as water, 
is so charged with fine bubbles that it appears to be milk white. 

Qas Evolution. — The evolution of gas, inevitable with storage 
batteries, is a distinct defect, and it is greatly to be wished that 
it were not inevitable. It changes the specific gravity of the 
solution by carrying off spray, makes the air of the battery room 
almost irrespirable, corrodes all brass or iron objects, and tends 
to produce external short-circuiting, by depositing a film of mois- 
ture on the outside of the cells and shelving. No ventilation 
seems adequate to overcome this trouble. The outside of glass 
cells should be kept dry; if of wood, oil can be applied to them 
to repel moisture. Such precautions as these operate to prevent 
leakage of current. Supports for the cells made of glass or 
porcelain are often used. Such are shown in Fig. 62. These 
contain oil in the shaded portion, but oil is not much used now. 



150 



ELECTRICIANS' HANDY BOOK. 



"petticoat" porcelain supports being used instead. Figs. 63 and 
64. One is placed under each corner^ 

All copper, brass, or iron should be excluded from the storage- 
battery room. Not only will these metals corrode, but there is 
always danger that the drip from them will get into the bat- 
teries and permanently injure them. Cables should be lead-cov- 
ered. 

The First Charge. — The first charging of a new battery should 
be at half or less than half the normal rate. Twenty or thirty 
hours may be given to it, instead of the normal eight hours. 

If the normal charging rate is unknown, it may be found by di- 




FiG. 63. Oil Insulating Supports fob Storage Battery. 





Figs. 63 and 64.— Petticoat Insulator for Storage Batteries. 



viding the ampere-hours of the battery by 8. A 400-ampere-hour 

battery should be normally charged by a _1!!2_ = 50-ampere cur- 

8 
rent giving 10 to 20 amperes for the first charge. 

Automatic Cut=Out or Circuit Breaker.— A danger always ex- 
ists in charging a storage battery. The voltage of the battery 
will rise, and that of the generator may fall, so that the battery 
will discharge itself through the generator, and will cause the 
latter to work as a motor. In some cases it may burn out the 
armature. 

To prevent this accident automatic cut-outs are used, which 
keep the circuit closed as long as a current is passing to the 



STORAGE BATTERIES. 151 

battery. Such operates by keeping the circuit closed until the 
current falls below a certain intensity. If it falls beiow this 
point, the circuit automatically opens. It will be found de- 
scribed under Circuit Breakers, Chap. XXVI. of this work. It is 
known as the underload circuit breaker. 

English Rule for Charging. — The English manufacturers al- 
low a charging current of 0.026 ampere per square inch of plate 
surface, and a discharging rate of 0.029. The charging current 
can be somewhat greater than the above without injury. 

Overcharge. — When the battery is charged, it is wasteful to 
give it any more current. An overcharge of as much as 20 per 
cent will not hurt the battery necessarily, but excessive over- 
charging often repeated will injure the plates. 

Prevention of Sulphaling. — If a battery is discharged and left 
standing, a whitish deposit, probably a basic lead sulphate, forms 
upon the plates. This interferes with the action of the battery. 
Plates so affected are said to be "sulphated," and the term, 
whether well chosen or not, must be accepted as a technical ex- 
pression. To avoid sulphating, 10 per cent to 20 per cent of the 
charge should be left in the battery. 

If plates are badly sulphated, there is often no other cure 
than scraping, which has to be carefully done to avoid injury to 
the plates. 

Sometimes a cell becomes short-circuited; dampness from the 
spray may bring it about, or bits of the plugs or active ma- 
terial from the plates, a fragment of the plate, or even some 
extraneous body may fall in and short-circuit a cell and discharge 
it before the operative suspects it. Such a cell will be in a fair 
way to become badly sulphated. 

Too strong or too hot an electrolyte will cause sulphating. 
The utmost permissible limit of temperature of electrolyte is 
125° F. (52° — C). Thus in charging a battery the current 
must not be so strong as to raise the temperature of the elec- 
trolyte to this degree; 100° F. (38°— C.) is a safer limit. 

If the sulphated plates are not badly affected, scraping may 
not be required. In either case the cell has to be slowly charged 
at not more than half the eight-hour or normal rate. The charg- 
ing must be greatly prolon^e-l. 



152 ELECTRICIANS' HANDY BOOK. 

If it is a single cell that is sulphated in a battery of a number 
of cells, if treated to an overcharge as described, the whole bat- 
tery will be overcharged with it. This is a bad practice, although 
occasionally it may be adopted. If the battery has clamped or 
bolted connections, the cell can be cut out during the discharge 
and connected during the next charge or charges only of the ' 
battery, so as to get a double or triple quantity of charging. An- 
other way, when cells are not permanently connected, is to give 
the defective cell a charging current during the discharge of the 
battery. To do this it must be disconnected, and its connec- 
tions reversed. The regular discharging current will then charge 
the cell so connected. This is not practicable with batteries with 
permanent connections. 

Sulphating uses up more or less of the active material of the 
plates. It is therefore a source of distinct injury, especially in 
such cases where mechanical treatment has to be resorted to for 
its removal. 

The presence of a small amount of sodium sulphate operates to 
get rid of the sulphating. A little of this salt (Glauber's salt) 
may be added to the sulphated cell, or a little sodium carbonate 
may be added, which is at once converted into sodium sulphate. 
After the plates are restored, the electrolyte must be removed, 
and the cell and plates washed down; the washings are removed, 
and new electrolyte introduced. 

5hort= Circuiting of Single Cells. — The operative must watch 
his battery. If he notices a change in color, finds a variation in 
voltage or in specific gravity in any cell, it is undoubtedly short- 
circuited. If the short circuit is due to any external cause, the 
trouble can be easily located as a rule. If a foreign body, such 
as a plug from one of the plates, has lodged between the plates, 
it must be removed. A rod of wood or of other non-conducting 
material, or a couple of such rods used like a tongs, may be em- 
ployed to pick it out. A strip of hard rubber with a hook at one 
end is excellent for this purpose. Sometimes a bit of the plate 
will project, and cause a short circuit. It must be crowded back 
or down. The plates should always be supported well above the 
bottom of the cells; sometimes they are at a height of six inches 
above it. Nevertheless, sediment may collect to a sufficient depth 



STORAGE BATTERIES. 153 

to touch the plates and short-circuit them. In the latter case the 
cell may be cleaned out, or the sediment if fine enough may be 
syringed or syphoned off without disturbing the upper layers. 
Then new electrolyte must be added to replace what has been 
removed. As has been before stated, a metal hook or wire should 
never be used in removing foreign bodies from cells. Cells 
should be most carefully watched for short circuits to prevent 
sulphating, which will occur if the short circuit continues. 

Sediment is sometimes removed by taking the plates out of 
the cell, syphoning off the electrolyte, and repeatedly flushing the 
cell with water and syphoning it off until the bottom is clean. 
But in large batteries the plates cannot be removed without 
danger of injuring the connections or bending them. 

Buckling. — A plate buckles or bends when the charging and 
discharging rate are excessive or when their action varies on its 
two faces. Sulphating may cause it if the white deposit forms 
only on one face, because, as already stated, sulphating inter- 
feres with the action of the plate. A buckled plate can be straight- 
ened sometimes. It should be placed between two boards, and 
heavy pressure applied. A few carpenter's wood screw clamps, a 
vise, iron screw clamps, or an improvised lever press may be 
used to give the pressure. Hammering is sometimes recommend- 
ed, but jarring is one of the worst things for plates, as it tends 
to detach the active material. Badly buckled plates may have 
to be discarded, if they crack badly on straightening. Buckling 
is apt to happen to automobile batteries when the temptation to 
take too much current out of them is yielded to. 

Disintegration. — Plates lose their active material, often on ac- 
count of sulphating; bits of lead may become detached; plugs 
may fall out; buckling with subsequent mechanical straightening 
loosens their structure. Anything that causes buckling is liable 
to cause mechanical deterioration. The expensive positive 
plates are more subject to such troubles than are the negative 
ones. 

Setting up a Battery. — Care in handling the plates and the 
securing of cleanliness are the great points to be observed in 
setting up cells. The plates will ordinarily come positives and 
negatives secured together in some shape, at least nested together. 



154 ELECTRICIANS' HANDY BOOK. 

so that on lifting with both connecting bars the positives and 
negatives will be handled like a single mass. Between the plates 
are placed insulators, strips of hard India rubber, wood, glass, or 
equivalent insulating material, and sometimes binders go around 
the bunch in addition. These elements must be examined, to see 
that no foreign substance is lodged between them. 

The cells must be perfectly clean. They are put in position at 
exactly the distance requisite to bring the connecting lugs to- 
gether. The supporting glass plates, if such are used, and the 
corner insulators must all be in their permanent positions. 

The elements are lifted into the cells, their supports, if such 
are used, being put in place. If there are loose insulators, these 
are put in also, and all is ready for connecting. If clamps or 
bolts are used for connecting, they should be painted or paraf- 
fined and wound with okonite tape. 

The positive and negative plates in a cell must not touch each 
other anywhere. If a lead-lined cell is used, the lead lining must 
not be in contact with any part of the elements. A single con- 
tact will be a step in the direction of a bad short circuit. 

The positive and negative plates are sometimes marked to dis- 
tinguish them, but their color will be a sufficient guide. The posi- 
tives are brown, the negatives gray. They must be put into the 
cells so as to bring the positive connections in one cell next to the 
negative in the next one. 

The electrolyte, perfectly cold, must be added in sufficient 
quantity to stand half an inch above the top of the plates. It 
should not be put into the ceils until all is ready for charging. 
If the plates stand uncharged in the acid, they w^ill become sul- 
phated. Therefore, as soon as the last cell is filled, charging 
should begin. The solution should be poured in with the greatest 
care to avoid splashing. Any that is spilled upon the outside of 
the cells or on the connections should be wiped off at once. The 
first charge should be at half normal rate for some hours, when 
it may be increased to normal rate. The first charging should 
be carried up to 2,6 volts, and the solution should be kept bub- 
bling for some time. For subsequent charging a voltage of 2.5 
is the proper limit. 

The manufacturers of storage batteries are always prepared 



STORAGE BATTERIES. 155 

to supply printed or special instructions for the operation of 
their batteries. Before setting up and putting a battery into 
action instructions should be obtained from the makers of the 
. battery. 

■ Preparing the Electrolyte. — This is a mixture of pure water 
r (distilled water is recommended) and pure sulphuric acid. About 
five volumes of water to one volume of chemically-pure sulphuric 
acid are used. 

If chemically-pure acid is not used, each carboy should be 
tested for hydrochloric acid, iron, and nitric acid. Other im- 
purities will be due to the new plates or to foreign substances 
finding their way into the solution. The acid is poured into the 
water; this is important, as, if the water is poured into the 
acid, a sort of explosive ebullition may occur, throwing the acid 
about. The mixture will be quite hot. After cooling it should 
read 1180 to 1250 on the hydrometer. It must be completely cool- 
ed before pouring it into the cells: 

A lead-lined vessel is probably the best in which to mix the 
solution, all things considered. Carboys will be liable to crack 
from the heat; enameled-iron vessels are perfectly satisfactory 
when new, but if the enamel is cracked iron will get into the 
solution. A glass or china water pitcher will answer for pour- 
ing the solution into the cells. 

Impurities in the Electrolyte and Tests. — It is so important 
to keep the electrolyte pure that the best practice is to use dis- 
tilled water to mix with the acid. The acid may contain im- 
purities. Hydrochloric acid and nitric acid are both injurious. 
Copper, iron or mercury salts are all injurious; some may come 
from drippings from iron or copper objects in the battery room. 
It is suggested sometimes to test the battery once a week for 
foreign substances. A few chemicals kept in solution in glass- 
stoppered bottles and some test tubes are all that is requisite for 
testing. Iron is detected by a solution of potassium ferricyanide; 
chlorine by a solution of silver nitrate; copper by a solution of 
ammonia. A little of the electrolyte is placed in the test tube, 
and a few drops of the reagent are added for the iron or chlorine 
tests. For copper, ammonia must be added and shaken with the 
solution in suflBcient quantity to give a slight odor of ammonia. 



156 ELECTRICIAN^ B' HANDY BOOK. 

or until red litmus paper dipped in the solution is turned blue. 
Iron gives a blue precipitate; chlorine a white one; copper a blue 
color. For testing for the presence of nitric acid, dissolve % 
gramme diphenylamine in 100 cubic centimeters of sulphuric acid, 
and add it to 20 cubic centimeters of water. A little of the sus- 
pected electrolyte is placed in a test tube, and a few drops of the 
reagent added. A blue color indicates nitric acid. For mercury, 
immerse a polished bit of copper in a sample of the electrolyte. 
A gray coloration on standing will indicate mercury. 

If nitric acid is detected, it must be got rid of, if present in 
considerable quantity. Sometimes the cells have to be flushed out 
with clean water and new electrolyte introduced. 

Nitric acid is more apt to be found in new batteries, where it 
has been used to corrode the plates before forming. The manu- 
facturers should see to it that no nitrates are present in plates 
that leave the factory. Chlorides are sometimes to be found in 
new chloride plates. Once a battery is running satisfactorily and 
has been found free from impurities, frequent testing should not 
be required. 

Indications from Gassing. — The evolution of gas, or "gassing," 
is an indication of completion of charge. The gassing of the 
cells should be watched. If at the end of a charge any cell or 
cells do not gas freely, it indicates that they are sulphated. 
When a voltmeter or hydrometer is not at hand, or when no ac- 
count has been kept of the ampere hours of a charge, the cells 
may be made to gas freely for twenty minutes, to make certain 
that the charge is complete. 

Cadmium Plate. — For testing the voltage of individual cells, 
a plate of cadmium attached to a wire is employed. The wire 
must be most thoroughly insulated, to prevent local action be- 
tween it and the cadmium. A preferable construction would be 
to use a plate of cadmium with a lug or extension, the whole in 
one piece, and thus avoid the necessity of having an insulated 
wire. The plate may be a couple of inches square. Cadmium in 
its electro-chemical relations lies between the positive and nega- 
tive plates of the lead plate storage battery, so that it is positive 
to one and negative to the other. It is used by inserting it in 
the electrolyte; a voltmeter is placed in circuit with the cad- 



STORAGE BATTERIES. 



157 



mium plate and the positive and negative plates alternately. The 
highest reading will be between the cadmium and positive plate. 
If the sum of the readings is 2.5 volts it indicates that the bat- 
tery is charged. A very low reading in the neighborhood of 
zero indicates a short circuit which must at once be attended to. 
The padmium plate should be wet before use, and no bubbles 
should be allowed to accumulate on it when in use, as they may 
vitiate the readings. 
Connections for Charging from Lighting Circuits. — The dia- 



POSITIVE WIRE 



+ POSITIVE WIRE 



NEGATIVE WIRE 



- NEGATIVE WIRE 



■ I 110 VOLT CIRCUIT 

K.S. 



It 



WI 




Fig. 6").— Charging a Storage 

Battery from a 110- volt 

Lighting Circuit. 



Fig. 66.— Charging a Storage 

Battery from: a 500-volt 

Lighting Circuit. 



gram. Fig. 65, shows the connection for charging from a 110-volt 
incandescent lamp circuit. At K S is a knife switch with safety 
fuses. Lamps enough, shown at L, are placed in parallel to give 
sufficient current, and the group is connected in series with the 
battery as shown. The combination is connected across the cir- 
cuit. Suppose the source is a 110-volt circuit, and that the 
name plate on the battery case or the manufacturer's instruc- 
tions give 5 amperes as the charging rate. A 110-volt 16 c. p. 
lamp takes I/2 ampere of current; a 110-volt 32 c. p. lamp takes 



158 



ELECTRICIANS' HANDY BOOK. 



1 ampere of current. Ten 16 c. p, lamps or five 32 c. p. lamps in 
parallel at L would give 5 amperes of current. 

The diagram, Pig. 66, shows the connection for a 500-volt cir- 
cuit. Here, owing to the higher voltage, five lamps are needed 
in series, and five sets in parallel at L to give 5 amperes. K S is 
the knife switch. 

In the diagram. Fig. 67, is shown the application of a rheostat. 
It must have current capacity to carry the charging current, and 
resistance enough to reduce to the requisite voltage. Suppose a 



■I- POSITIVE WIRE 



-NEGATIVE WIRE 



— (EMC^ 



n < 



10-500 VOLT CIRCUIT 




ARC LIGH.T CIRCUIT 




Fig. 67. -Charging a Storage 
Battery with a Rheostat. 



Fig. 68.— Charging a Storage 

Battery from an Abo 

Light Circuit. 



battery is to be charged at 6 volts from a 110-volt circuit at a 

rate of 5 amperes. By Ohm's law we have: 

110 — 6 volts 

— = 20.8 ohms. 

5 amperes 

The rheostat must be set at 20.8 ohms resistance. 

Charging from the incandescent light system is said to be a 
cheap way of charging. If there are cells enough to absorb 100 
volts in the charging, it is an efficient way of charging; if there 
are but a few cells, absorbing 10 to 20 or 30 volts only, it is ex- 
ceedingly inefficient, and the sight of a lot of lamps glowing to 
secure the charging of a small battery will always be repugnant 



/ 

STORAGE BATTERIES. 159 

to an engineer. Yet as the lighting companies sell current rather 
than watts, it may be economical if not efficient to charge bat_ 
teries as described. 

The diagram, Fig. 68, shows the connections for charging from 
an arc light system. Here absolute danger to life is present. 
The arc light circuit should only be used by perfectly competent 
persons, and the greatest care should be exercised. All perma- 
nent connections should be made when the circuit is dead. L L. 
indicate arc lights, R a resistance, and C S a consumer's switch. 
The peculiarity of this switch is that the contact arm A is so 
wide that in swinging it is always in contact with one or with 
two of the contact studs, D, C, and B. In the position shown it 
is in contact with D and C. Almost all the current goes by way 
of D; a little, following the law of parallel circuits, goes through 
the resistance R. Let the switch be swung to the right. It first 
leaves D, keeping in contact with C, and the lighting current 
all goes through the resistance R. It next, without leaving C, 
makes connection with B, Again the law of parallel circuits 
comes into play, and the current divides itself between the re- 
sistance R and the battery; the knife switches KS are supposed 
to be closed. If they are open, the whole current will go through 
the resistance R. 

Suppose the line current is 7 amperes, and that the battery re- 
quires 5 amperes, and absorbs 6 volts in charging. Then by 
Ohm's law the resistance R is given by the formula: 

6 volts 

= 3 ohms. 



7 — 5 amperes 

If the line current is less than the charging current, as the lat- 
ter is specified by the manufacturer of the battery, the arm 
may be swung so far as to rest on B only. Stops must be pro- 
vided, so that it is impossible to swing it so far to right or left 
as to break contact with B or D respectively. 

The Polarity of the Circuit must be determined with abso- 
lute certainty before using. Otherwise the battery plates may 
be ruined. In testing the arc light circuit for polarity, the con- 
tact arm A must rest on both B and C. 

The usual test is to dip wires connected to both leads of the 



160 ELECTRICIANS' HANDY BOOK. 

circuit into a glass containing solution of salt in water. The 
wires must be held about an inch apart. Bubbles of gas will be 
given off in greater quantity from the negative pole. This lead 
is connected to the gray or negative plate of the battery. In 
attempting this test with an arc light circuit, be exceedingly 
careful to use heavily-insulated wires. It is best to handle them 
by having them tied to the ends of two dry wooden rods a couple 
of feet long. 

The experience of the last two decades of electric development 
has cured of bravado all electricians worthy of the name. The 
greater a man's experience, the more careful will his manipula- 
tion be. 

Taking Out of Service. — When a battery is to lie idle for 
some time, it must first be charged at the normal rate. The 
electrolyte is then syphoned off and replaced by water. The 
electrolyte may be saved. Clean carboys are the best receptacles 
for preserving it. The cells are then filled with water imme- 
diately, and the battery is allowed- to discharge until its potential 
falls below one volt. The discharge should be as nearly as pos- 
sible at the normal rate. The replacement of the electrolyte by 
water will tend to increase the internal resistance, and to dimin- 
ish the rate of discharge. After the battery is discharged, the 
water is removed, and the plates and cells are allowed to dry. 
In the case of small clamp or bolt connected batteries, the plates 
may be removed and the cells washed out and dried. The plates 
may be stored in the cells or elsewhere as desired. Dryness is 
the great point, and is very hard to insure unless the plates can 
be removed from the cell, so as to admit of drying it out before 
replacing the plates. The plates can be stored in any dry place, 
but should be handled with the greatest care. 

Another method of putting a battery out of service is the foJ 
lowing: The battery is first completely discharged at a low rate 
The elements are at once removed from the cells and put intc: 
water. The cells are emptied, the solution being saved. The cells 
are washed out and filled with clean water, and the elements are 
replaced. The water must stand over the top of the plates. 

The above method can be carried out with a permanently con- 
nected battery by the use of a syphon. The solution is syphoned 



STORAGE BATTERIES. 161 

off and stored in carboys. Water is poured into the cells and 
syphoned out two or three times, and the cells are eventually 
left filled with water. 

Cells. — The cells of storage batteries are for small and moder- 
ate sizes generally made of glass. For special purposes, such as 
automobile service, hard-rubber cells may be used. For large 
sizes and for central station and similar work they are often 
made of wood lined with lead. In the latter great care must be 
employed in setting up, to prevent the plates touching the lead 
lining, as this would give a short circuit if both negative and 
positive touched it. Acid-proof paint is used to paint the wooden 
cells. 

Insulation of Cells.— This must be carefully looked after. 
The surface on which they rest may be covered with heavy 
sheet glass, or porcelain or glass insulators, already described, 
may be used to carry them, one under each corner. If the cells 
are of glass, a board painted with acid-proof paint should be pro- 
vided for each one, and this should rest upon the four corner 
insulators. The insulators may be kept in place by being pinned 
to the floor with wooden pins set in melted sulphur. 

Making Battery Connections.— By far the best jnaterial for 
permanent connection is lead applied by what is technically 
termed "burning." Soft solder, which is an alloy of lead and 
tin, is recommended sometimes, but is only a makeshift. 

For temporary connections, bolts or clamps may be used. 
These are objectionable, as they may introduce copper or other 
impurities into the cells. Everything in a battery room is ex- 
posed to the spray of dilute sulphuric acid. Lead is unattacked 
by it, and is the ideal connecting and protecting substance. 

If two strips, from two sets of plates, for instance, are to be 
connected, their ends are cut off at an angle of 45° with the 
vertical. The acute corners are at the bottom of the strips. The 
oblique faces are scraped off with a plumber's scraper, the two 
sharp corners are brought together, and a clamp or trough of 
sheet iron is sprung on from the bottom. The cut. Fig. 69, may 
be referred to here. The strips must lie horizontally and in 
line. Thus a V-shaped cavity with its sides closed by the iron 
clamp is produced. 



162 ELECTRICIANS' HANDY BOOK. 

A blowpipe flame, best of hydrogen gas, although illuminating 
gas may be used, is the heating agent. A bar of lead is held 
over the V-shaped chamber and is melted by the blowpipe flame 
until enough drops off to fill the cavity. The flame is applied 
alternately to the bar and to the surfaces of the cavity. If hy- 
drogen gas is used, no flux is- needed; if illuminating gas, a 
little tallow will be required as a flux. 

The surface of the cavity should be kept just at the melting 
point, so that as the melted lead drops in, it and the lead strips 
will melt together. When the chamber is filled drop by drop, 
with heating of the surfaces during the process, the result 
should be a homogeneous bar of lead. The least excess of heat 




Fig. 69.— Storage Battery PiiATE Lugs and 
Soldering Clamp or Trough. 

may melt the strips outside the limits of the clamp, and too 
little heat will make the process a failure. 

The flame should be a small blue one. The apparatus can be 
bought at dealers in machinists' supplies. 

When a number of lugs from plates are to be "burned" to a 
lead bus-bar, such as shown in the cut. Fig. 70, a sort of spring 
clamp or tongs is used whose outer ends are beveled to fit the 
slope of the bus-bar. Referring to Fig. 70, B is the joint in the 
spring clamp and F is the spring forcing its other end together. 
D is the top of the bus-bar whose section is shown above at B. 
A A are the lugs from two plates in adjoining cells. C is a plate 
beneath the bus-bar holding all in line. 

The lugs to be connected are beveled off and the spring clamp 
is put on, and the beveled ends are placed against the bus-bar. 
The acute or lower angle of the strip or lug must touch the 



STORAGE BATTERIES. 



163 



bottom of the bus-bar. This gives a V-shaped cavity just as be- 
fore. The surfaces are scraped before the spring clamp is put on. 

Lead is melted in as before. This is a more critical operation 
than the other. A slight excess of heat will ruin the bus-bar. 

If there are seams or drops of lead solidified on the pieces 
joined, they can be trimmed up. A good joint is almost indis- 
cernible. 

Neatness should not be sacrificed to strength. The joints may 
with advantage be left a little larger than the lugs or strips. 




Fig. 70.— Soldebi^'G Storage Battery Pirate Lugs to 
Bus- Bab with Lead. 



The principle of soldering is the uniting of two metals by an 
alloy more fusible than either. In "lead burning," which has 
just been described, the fusibility of the lugs, bus-bars, and lead 
used to unite them is the same. In this feature the difficulty of 
doing it inheres, and the same feature occasions constant risk of 
injury unless the operative is experienced and competent. 

Practical Notes, — On unpacking a storage battery, the cells 
must be cleaned and examined to see if they are tight. Wooden 
cells must be tried by filling with water. 

Shelving must stand clear of the walls, and must be insulated 
from the fioor by glass plates or porcelain blocks. 

Every fourteen days the battery should be charged up to the 
full charge, and then with half the normal current for a half 
hour. The battery should never be left uncharged for over two 



164 ELECTRICIANS' HANDY BOOK. 

days. Batteries unused for longer periods and which have stood 
idle are brought gradually into service by strong charging. 

In slow discharge with small current intensity, not only the 
voltage but the specific gravity of the solution must be watched. 
The latter is reduced in such cases relatively more quickly than 
in rapid discharge. When it sinks below 1.15, the battery must 
be recharged, although the voltage may not be down to its allow- 
able limit. 

The acid in all the cells should have the same specific gravity, 
or else they will not all gas together. Equalizing the specific 
gravity by adding water to the cells which need it must be done 
when the battery is fully charged. 

At least once a week cells should be examined for short cir- 
cuits. Glass cells can be examined by holding a lamp behind 
them, so as to see if anything, such as a paste plug, has fallen 
between the plates. Incandescent lamps used for this purpose 
should have cages. Special lamps are provided for inserting into 
the fluid in larger cells of opaque material. 

Foreign bodies, buckling of the plates, and bits of the plates 
or pasting can be the causes of short-circuiting in the cell. For- 
eign bodies must be removed by a rod of wood, glass, or hard 
rubber. The latter is the best. In pulling out the piece, care 
must be taken not to displace paste or otherwise injure the 
plates. On the next charging, the plates which were short-cir- 
cuited can be watched to see if they gas properly. The ab- 
sence of gas bubbles at the end of a charge indicates a short 
circuit. Never use a bare wire to remove anything from the cells. 

End Cells. — This is a technical term for cells at the end of a 
storage battery, which are thrown in or out of circuit to regulate 
the voltage. A storage battery loses during the discharge over 
half a volt potential. If there are fifty-two cells in circuit, 
each one giving 2.2 volts, the total voltage will be 52 X 2.2 = 
114.4 volts. As the battery delivers current, the voltage will 
gradually fall. At 2 volts it would give only 104 volts. If 114 
volts is the station voltage, the first voltage named would answer, 
as the excess of 0.4 volt would not be too much. To maintain it, 
cells would have to be added in series. Thus at the 2-volt poten- 
tial 114 -^ 2 = 57 cells would be required in series. When the 



STORAGE BATTERIES. 165 

battery was ready for recharging, it would give only 1.8 volt per 
cell, and to maintain the station voltage 114 -4- 1.8 = 63 cells 
would be required. This number would give a fraction less than 
114 volts. 

In the case assumed, the freshly-charged battery would start 
off with 52 cells in series. As the voltmeter fell, due to the bat- 
tery losing electromotive force, a cell would be thrown into cir- 
cuit. The addition of a single cell would add about 2 volts to 
the potential. Therefore the potential should be allowed to fall 
about a volt before putting another cell into series. 

A bus-bar with traveling connecting springs is provided for 
throwing cells into and out of series. This is quite an elaborate 
piece of apparatus in large installations, in which the traveling 



:^E 



Fig. 7',— Counter Electrom ttve Force Cells. 

contacts are sometimes operated by electric motors. For small 
installations switches may be provided for turning cells on and 
off. 

End-cell regulation is very imperfect, as it involves a sudden 
change of two volts or thereabout every titne a cell is thrown 
into circuit. 

Counter Electromotive Force Cells. — The elasticity of action 
of the floating storage battery, when used in combination with a 
dynamo plant, is increased by the use of unformed lead plate-sul- 
phuric acid cells, which are thus entitled. In the diagram. Fig. 
71, D represents a dynamo, B a storage battery, and A counter 
electromotive force cells. When the dynamo is running so as to 
charge the batteries, it delivers current to the working circuit 
and forms or charges the counter E. M. F. cells, and therefore 
has to be run at a higher voltage than is received by the circuit. 



166 ELECTRICIANS' HANDY BOOK. 

on account of these cells operating against it, by absorbing volt- 
age. This extra potential forces current through the battery B, 
so that it is charged at the same time that the district or working 
circuit is being supplied. When the dynamo is stopped, the main 
battery B supplies the lamps or other appliances. The counter 
E. M. F. cells are cut out one by one as the voltage due to the 
main battery falls, and thus serve the purpose of end cells. 
Seven counter E. M. F. cells suffice for charging the battery when 
few lamps are in use; as many as eighteen may be needed when 
a quantity of lamps are being lighted. 

Floating Battery. — A storage battery connected across the 
leads of a parallel system, so as sometimes to be charged by the 
generating plant and sometimes to give current to the system, is 
called a floating battery. If it were not for the variation in 
voltage of the storage cell combination, it might operate auto- 
matically, but a storage battery needs constant watching, and 
the coupling and uncoupling of end cells and other minor man- 
ipulations required are very simple. 

Charging Plant Operation. — Start the dynamo with all due 
precautions as to oiling and the other details. 

The automatic cut-out is thrown into circuit. The operative 
by a current indicator must satisfy himself that the current is 
going in the right direction. The ammeter must be observed, to 
see if the proper intensity of current is being given. The volt- 
age and amperage are regulated by the speed, or by a rheostat. 

During the charging the underload circuit breaker must be 
watched, to see if it is in sensitive working order. It can be 
tested by opening and closing the main circuit. As the charging 
progresses, the electromotive force of the battery, which is, of 
course, counter to that of the dynamo, increases, and the circuit 
breaker will eventually fly open if the electromotive force of the 
machine is not brought up. If this cannot be done, one or two 
cells can be cut out of the series. 

When the charging is complete, the main switch is opened; the 
motor engine or electric motor is attended to lest it should 
start racing; resistance is thrown into the field circuit, which is 
eventually opened ; the brushes are lifted off the commutator, and 
all is brought to rest. 



CHAPTER VIII. 

THE FIELD OF FORCE. 

The Field of Force. — A current of electricity produces a con- 
dition which is attributed to a strain or whirl in the ether. The 
locality or locus of the condition, as far as its detection by ordi- 
nary means is concerned, is in the vicinity of the current, and 
unless distorted in some way, the locus is symmetrical with re- 
spect to the current. To the mind the locus is best pictured as a 
cylinder through whose center the current goes. The locality is 
termed a field of force, and its place is called the locus. It affects 
iron, and is traced and may be located by 'its effects upon the 
compass needle or upon iron filings. It is no imaginary con- 
ception, for it is by virtue of the field of force that every dynamo 
electric generator and every electric motor works. A needle 
held near a magnet is attracted because of the field of force. The 
needle of the mariner's compass is acted on by the earth's field 
of force. A coil of wire rotated away from any artificial field 
of force generates electromotive force as its convolutions sweep 
through the earth's field of force. The armature of every gen- 
erator produces currents and potential, which do an enormous 
quantity of work for humanity, entirely through the agency of the 
field of force. 

In its effects it is a very tangible and real thing; in its theory 
it has to be somewhat imaginary. 

Ether and Current. — A current of electricity is assumed to 
establish a species of strain or tension upon the ether, which 
strain is only detectable in the vicinity of the conductor. Theo- 
retically, every current affects the ether through all space. A 
conductor through which a current passes is said to be sur- 
rounded by a field of limited size, because the intensity or 
strength very rapidly diminishes as its distance from the wire 



168 



ELECTRICIANS' HANDY BOOK. 




.1,^^^ 



increases. It is the field in the vicinity of the conductor which 
is easily detected. A short distance from the conductor no field 
can be detected, except by very delicate instruments. 

Detection of the 
■■l??^^^'P?!Flff!P?«'f5F?i?T?'T'^^^ Field.— If a conductor, 

through which a strong 
current passes, is led ■ 
upward through a sheet 
of paper upon which 
iron filings are sprink- 
led, they will arrange 
themselves in a more or 
less close approach to 
a series of concentric 
circles having the con- 
ductor where it goes 
through the card for 
their common centers, 
as shown in Fig. 72. 
The filings are more 
crowded near the wire 
than on the edges of the outer circles, indicating a weakening of 
the ether strain as the wire is more distant. The paper may be 
shifted up and down the wire, and the effect will be the same 
at all places. The filings indi- 
cate the existence of a state of 
ether strain, which in general 
terms may be described as a 
cylindrical field of force. The 
experiment is illustrated in the 
diagram, Pig. 73. 

A compass needle held near a 
horizontal conductor in the mag- 
netic meridian, through which 
conductor a current is passing, is 
deflected by the same cause which 
affects the filings. 

The intensity of the field of force must be described in some 



Fig. 73.— Lines op Force Purroukding a 
Conductor Shown by Iron I ilings. 




Fig. 73.— Diagram of Experiment 
WITH Iron Filings. 



THE FIELD OF FORGE. 



169 



way, and the method adopted is to treat the field of force as a 
collection of lines of force. If a field is ten times as strong as 
another, it is said to have ten times as many lines of force in a 
given area. 

Referring to the cuts, Fig. 74 shows the conception of the lines 




Fig. 74.— Likes of Forcte Surrotindtng an Active Conductor. 



of force surrounding an active conductor. Fig. 75 shows the 
cross-sectional view of a conductor A through which a current 
is passing. 

Lines of Force Produced by a Curved Conductor. — The effect 
of curving a conductor is to bring the circular lines of force to- 
gether. The parts of the circles be- 
tween adjacent turns are of opposite — 
polarity, and annihilate each other, 
and within and without the course of 
the conductor, lines of force such as 
shown in Fig. 76 are produced. The 
cut will be again referred to when the 
significance of N and S in it will ap- 
pear. 

notion of a Conductor in a Field 
of Force. — A conductor which is swept 
through a field of force so as to cut the 
lines of force has electromotive force 
impressed upon it, and a current will 
go through it, if its ends are joined so 

as to form a closed circuit. A current of electricity is considered 
or conceived of as electricity in motion. It is consistent to find 
some motion inherent in an apparently fixed and immobile line 
of force. 

Accordingly, the line of force with absolutely fixed direction 






\^^ 



Fig. 75.— Lines of Force 

Surrounding av Active 

Conductor. 



170 



ELECTRICIANS' HANDY BOOK. 



may be assumed to have a whirling motion around its axis, the 
latter never changing. The cut, Fig. 77, shows a circular line 
of force, in which the whirl is indicated by arrows. The fa,miliar 
smoke ring sometimes seen rising from a locomotive's smokestack 
has this whirl. 

The whole subject is to be treated as a group of analogies 
rather than theory. 

Direction or Polarity of Lines of Force.— In electricity there 
are strict relations that it is impossible to summarize or theorize 
upon without appealing to assumed motion and direction. Po- 
larity, which is certainly direction, is familiar to every child 
in the north and south poles of his magnet. The magnet is 




Fig. 76.— Lines op Force Produced by Circular 
Current. 




Fig. 77.— Smokb 
Ring. 



the most familiar producer of lines of force, and their polarity 
or direction is fixed by assuming that they pass through the 
steel of the magnet from the south pole to the north pole, issue 
therefrom, and curving around through space return to the south 
pole. The electric current is already fixed as regards direction 
by assuming that when produced by the galvanic battery, it 
starts from the copper or corresponding plate and goes through 
the outer conductor to the zinc plate. Assume that a current of 
electricity is passing through a conductor pointing directly at 
us. If the current is coming "end on" toward us, the lines of 
force surrounding it will be in planes at right angles to the 
wire and may be circular or otherwise, but will form closed lines 
around the conductor. Their direction or polarity is expressed 
by saying that it is opposed to the motion of the hands of a 



THE FIELD OF FORCE. 



171 



watch or clock. It is anti-clockwise. If the current were going 
away from us, the polarity of the lines of force would correspond 
with the motion of clock hands; their polarity would be clock- 
wise. 

If a current passes through a spiral conductor, such as shown 
in Fig. 78, in the direction indicated by the small arrows, the 
direction of the lines of force produced will be shown by the 
large arrow. Going back to Fig. 76, page 170, the same relation is 
indicated by arrowheads on its lines. 

If the central arrow in Fig. 78 indicated a conductor passing 
a current in the direction of the arrow's pointing, and the 




Fig. 78,— DiBECTioisr op Lines of Fobck Produced by a 
CiKCULiAR Current. 



spiral was of iron, lines of force would produce the polarity 
shown by the arrows. 

flemoria Technica for Lines of Force. — If a current is flow- 
ing directly away from us, it may be taken as representing the 
flight of time. The lines of force surrounding it therefore have 
the direction of the motion of the hands of a watch, which in- 
dicate the flight of time. 

Utility of the Conception of Lines of Force,— The conception 
of lines of force is most useful; and Faraday, one of the loveliest 
characters and greatest geniuses on the scientific horizon, did the 
greatest service to science in his conception of them. An ap- 
proximation to correctness seems sometimes more useful than 
the bare truth, and the bare truth in this case is that there are 



172 ELECTRICIANS' HANDY BOOK. 

no lines of force, but there is a volume of force. The entire space 
surrounding a current of electricity is affected or polarized by it. 
The current acts upon space of three dimensions or volume, not 
upon space of one dimension, which is the line. An infinite num- 
ber of lines make space of three dimensions just as a great num- 
ber of the thinnest filaments can build up a thick cable. 

The field of force varies in strength with its proximity to the 
current, and theoretically each current affects all space. Prac- 
tically, the field near the conductor is the only part strong enough 
to play any part in economics. This strength is expressed by 
saying that there are more lines of force per given cross-sectional 
area near the conductor than far from it. 

Density of a Field. — The adjective "dense" and the noun 
"density" are the best words to use to specify the strength of a 
field. As the strength of a field is measured by the relative 
number of lines of force in a given cross-sectional area of it, 
and as it is taken as being made up of lines of force, its density 
expresses exactly its relative quantity of lines of force. 

The Magnetic Circuit. — The entire course taken by lines of 
force must be a closed curve, such as a circle or ellipse. In the 
field of force maintained by a horseshoe or U-shaped magnet, the 
lines of force go through the magnet as well as through space 
outside it. Their path may approximate a circle or an ellipse, 
or be a combination of various lines and curves, but the path 
must be continuous. A line of force which extends out into 
space without limit, or a line of force which is straight for its 
entire length, is impossible. 

The closed path followed by lines of force is called the mag- 
netic circuit, and is shown by the dotted lines. Fig. 76, on page 170. 
It is closely analogous to the electric circuit. 

Energy and the Hagnetic Circuit. — A fundamental difference 
exists between the electric and magnetic circuits. 

A constant electric current develops energy upon its circuit, and 
energy has to be expended to maintain it. Lines of force are main- 
tained in their circuit without the expenditure of any energy. En- 
ergy is indirectly expended upon the maintenance of the field of a 
dynamo, simply because an electro-magnet is preferred to a nat- 
ural magnet in such machines. It enables a machine to be made 



THE FIELD OF FORCE. 173 

smaller than it would be were a natural magnet used. A natural 
magnet maintains a field of force indefinitely, without expending 
any energy. 

Counter and Forward Electromotive Force. — To create new 
lines of force requires the expenditure of energy; if lines of 
force go out of existence, they develop energy in so doing. Every 
current in a given circuit maintains lines of force proportional 
in number to its intensity. Energy has to be expended to bring 
these lines of force into existence, which opposes any increase 
of current, and this opposition is called counter electromotive 
force. If the current tends to cease, the lines of force in dis- 
appearing develop energy and tend to increase the current. 
This action is called forward electromotive force. 

Increasing the strength of a field is done by increasing the 
number of lines of force in it, and decreasing the number of 
lines of force decreases the strength of a field. Energy is re- 
quired for the increase, and energy is given off in the decrease. 

Building up the Field of Force. — The action of an increasing 
current in producing new lines of force is called building up a 
field of force. When a circuit with a battery or other generator 
in it is closed, so that a current passes through it, it has to build 
up a field of force, and this action absorbs energy. When the 
field is built up, the full current due to the electromotive force 
passes through the circuit unopposed except by resistance, and 
maintaining the field without expenditure of energy. 

Energy is expended in building up a field of force, none is re- 
quired to maintain it. To take a homely comparison, energy is 
expended in carrying a weight up a flight of stairs. Once up the 
stairs, it is maintained there without any expenditure of energy. 

Potential Energy of the Field of Force. — Energy seems, there- 
fore, to have disappeared or to have been annihilated, which is 
impossible. The energy expended in forming the field of force 
is stored up in it. A field of force can be compared to a storage 
battery. In it is stored up electric energy of the potential type, 
which energy is expended in the production of kinetic electric 
energy when the field goes out of existence. This disappearance 
of the field takes place when the current ceases. Then the lines 
of force disappear at a more or less rapid rate, and as they do so 



174 ELECTRICIANS' HANDY BOOK. 

develop forward electromotive force, which, as we have seen, is 
of the sense or polarity of that which actuated the original cur- 
rent, and this forces additional current through the line. The 
energy of the field appears in the form of electromotive force 
quantity units — volt-coulombs or some multiple or fraction of 
them. 

Energy and the Field of Force. — In recapitulation it may be 
repeated here that (a) energy is expended in building up a 
field of force; (&) that no energy is absorbed in the maintenance 
of a field of force; (c) that energy is developed in the destruction 
of a field of force. As a corollary from the above, it follows 
that (d) a field of force is a seat of potential energy. 

Nature of the flagnetic Circuit.— A magnetic circuit is com- 
posed of a continuous path through space traversed by lines of 
force. The path must be continuous, and the lines of force must 
be closed or re-entrant curves, circles, ovals, and the like. No 
break can be made in the circuit; there is no such thing as an 
open magnetic circuit, strictly speaking. 

The subject presents many analogies with the electric circuit 
and its phenomena. The lines of force are analogous to the 
current, and the current of electricity flowing at right angles to 
some part of their course, plays a part so like that of electromo- 
tive force, that its action is sometimes attributed to magnetomo- 
tive force. For the passage of an electric current, a conductor 
of some sort is required. All forms of matter can be broadly 
divided into relatively very good and very poor conductors of the 
electric current. For lines of force no such broad distinction 
can be drawn. Air or a vacuum is the worst conductor, but is a 
fairly good one at that. Iron is the best conductor, yet as the 
field grows intense, and more and more lines per unit area pass 
through it, its relative superiority over air or a vacuum dimin- 
ishes. 

The electric current passes through a conductor in intensity 
proportional to the electromotive force urging it. This follows 
from Ohm's law. Lines of force pass through air or a vacuum 
in proportion to the magnetomotive force urging them. The 
law of the magnetic circuit in a vacuum or in air is exactly 
analogous to Ohm's law. 



THE FIELD OF FORGE. 175 

There is very little difference in substances as regards their 
capability of passing lines of force until iron is reached, when at 
,once there is a great difference; for iron may have over three 
hundred times the power of passing lines of force which air has. 
Permeability and Permeance. — The specific or relative con- 
ducting power of a substance for lines of force is called its 
permeability. The conducting power of a given magnetic circuit 
is called its permeance. 

Iron and the Field of Force. — Among all the forms of matter, 
iron stands alone in its relations to lines of force. Recurring to 
a comparison with electric current laws, it is as if copper was 
several hundred times a better conductor than other substances; 
as if there were no practical insulator for electric currents; and 
as if all substances except copper possessed equal conductivity. 
The difference between the laws of the field of force and of the 
electric current extends still further than the above would indi- 
cate. 

Saturation. — Iron becomes a relatively poorer conductor for 
lines of force as more are passed through it. As the lines of 
force produced in iron increase in number per unit area, and are 
more and more thickly crowded together in it, the iron is said 
to approach saturation. 

The permeability of iron decreases as it approaches magnetic 
saturation. 

The permeability of air, of a vacuum, or of gases in general is 
virtually constant. 

Different qualities of iron have different relative powers of pass- 
ing lines of force — they vary in permeability. 

Naturally, a thick piece of iron passes lines of force better 
than a thin one. It possesses better permeance. As long as the 
same density of field (lines of force per unit area) exists in the 
iron, it is subject to an analogue of Ohm's law. 

Three Factors of the Magnetic Circuit. — There are three 
factors to be understood. They are so often referred to, that 
their symbols have become fixed in the science. These symbols 
are H^ g^ and n. The last is the Greek letter m and is pro- 
nounced "mu." The \-\ and B ^^^ invariably printed with full- 
faced type. 



176 ELECTRICIANS' HANDY BOOK. 

riagnetic Force. — This is sometimes called magnetomotive 
force, and is indicated by the letter H It is the cause of mag- 
netism, and can be regarded as an effect of the electric current. 
As developed and used in electric machinery, it is almost al- 
ways due to electric current in circular or spiral conductors. It 
is produced in dynamos and motors by passing an electric cur- 
rent through wire conductors wound around iron cores. The 
permeance of the cores, due to the permeability of the iron, gives 
a good path for lines of force. 

Ampere Turns. — The current is measured in amperes and the 
turns of wire are counted. Multiplying them together, we have 
ampere turns. Electro-magnets are excited by ampere turns; the 
magnetizing force acting on them is often measured by ampere 
turns; however this force is measured, it is rigorously propor- 
tional to the ampere turns. 

H may be expressed as lines of force, or as ampere turns, as 
a matter of convenience. The latter seems too concrete, but it 
is easily referred to the line of force, because the ampere turns 
multiplied by 1,257 gives the value of H in C. G. S. units. 

This magnetizing or magnetomotive force acting on a mag- 
netic circuit sends lines of force through it, each one being taken 
as representing a continuous curve. The whole set resemble as 
drawn a set of oblong or of other shaped rings. 

Field Density. — The density of a field of force is indicated by 
the letter g always printed in full-faced type. It denotes the 
effect of |-|, which, as has been said, may be given in ampere 
turns. An equation similar to that of Ohm's law expresses the 
relation between H and B- It is: 

R_ H 

D — reluctance 

B is the number of lines of force which a given magnetic force 
H can force through a unitary cross-sectional area of a given 
magnetic circuit. 

As the specific reluctance or reluctivity of air is unity, and 
remains so for all values of g ; in an air path H and B vary in 
direct ratio with each other. If H is doubled, B is also doubled; 

p 

the ratio — = 1 holds for air. 



THE FIELD OF FORCE. 177 

Permeability.— The relative conducting power for lines of 

Q 

force is so called, and is expressed by H. The permeability of air 

H 
is equal to 1. Permeability is the reciprocal of reluctivity or of 

p 
specific reluctance. For iron rj exceeds unity except possibly for 

H 
very high values of H because iron has higher permeability than 
air for all ordinary values of H. 

Q 

The quotient S jg expressed by /n (mu) or 

" = // = permeability. 

This reads like Ohm's law, but is destroyed by the properties of 
iron, by which there are different values of fi for different values 
of B. -A-S B increases, ^ diminishes for iron, never reaching but 
approaching unity. 

Saturation of Iron. — The permeability of iron approaches 
unity as its field density increases. When permeability is equal 
to unity, iron is theoretically saturated. Saturation indicates 
the disappearance of the relative superiority of iron over other 
substances as a path for lines of force. The analogy with Ohm's 
law does not hold with iron until saturation is reached. 

In practice iron is said to be saturated long before this 
value is reached. The practical saturation of iron is reached 
when jii is less than 500. In wrought iron such imperfect 
saturation is reached at 125,000 lines to the square inch as a 
value for B ' ^^^ ^^^^ iron, at about 70,000 lines. 

No Insulator of Magnetism. — There is no insulator of mag- 
netism. Perpetual motion has in many a poor inventor's mind 
appeared a possibility if an insulator of magnetism could only 
be found. 

The line of force is an independent sort of being. "Water 
projected from a pipe takes a parabolic course through the air 
unless it strikes a wall or something which will deflect it. An 
electric current follows its conductor as long as it is continuous. 
When the wire carrying it is cut or a switch is opened, the 
current is stopped. 

When a magnetizing force, ^, is brought into existence, lines 



178 ELECTRICIANS' HANDY BOOK. 

of force go on their circuits and cannot be stopped by any mate- 
rial which intervenes. Metals, organic material, water, all 
things, are alike powerless to stop them. 

The Qauss.— Air is the standard for the magnetic circuit. 
A magnetizing force, H, of intensity to force one line of force 
per square centimeter through one centimeter thickness of air 
is termed a "gauss." If the force, H. is doubled, two lines of force 
will pass per square centimeter, and so on. One gauss is equal 
to 0.7955 ampere turn. 

Reluctance and Reluctivity. — The material of the path of 
the magnetic circuit resists the passage of lines of force, and 
is said to possess reluctance. The relative reluctance of differ- 
ent materials is reluctivity. The latter word is very little 
used. Everything in nature possesses reluctivity. That of air, 
being taken as the standard, is given the value of 1. Reluc- 
tance and reluctivity are the reciprocals of permeance and 
permeability respectively. 

Synonyms for B, H, ^^d //. — Different authors have given so 
many names to these three quantities that the first two are 
very often spoken of as "g" and**H." The principal synonyms 
of B are the following: Field density, flux density, magnetic 
displacement, internal magnetization, magnetic induction, per- 
meation. Of H the following are the principal: Magnetizing or 
magnetic force, rate per centimeter of fall of magnetic potential, 
magnetomotive force. Of ji the following are the principal: 
permeability, specific conductivity for lines of force, magnetic 
multiplying power. 

The curves expressing the relations of magnetic force H 
and field density g are often calle'^ Q and H curves. 

B and H Curves. — The relations of B to H constantly chang- 
ing are best shown by curves. The diagram. Fig. 79, gives 
curves for various kinds of iron. The horizontal line gives- 
values of H, the vertical one gives values of B- As the values 
of B ^^® much larger than those of H^ the diagram is al- 
ways magnified in the horizontal direction. If this were not 
done, and the scale were made the same for both B ^^^ H 
values, the diagram would be awkwardly high and narrow, and 
the H values could not be read with any degree of accuracy. 



THE FIELD OF FORGE. 



179 



An air diagram would properly be drawn without distortion. 

Q 

A ~2 = 1 for air, th^ "curve" for it would simply be a straight 
line rising at an angle of 45° with the horizontal. On the dis- 
torted diagram, Fig. 79, the air line would be almost horizontal. 
When it would cross the iron line, the point would be reached 
when air would be more magnetizable than iron. This point, it 
is safe to say, never has and probably never will be reached. 

Interpretation. — The curves indicate the locus of points where 
any magnetization B is produced by any magnetizing force H. 



16000 



(2000 



8000 



4000 




5 10 20 30 40 50 

Fig. T9.- Magnetization Curves of Iron and Steel. 



A vertical erected on any given point on the line H will inter- 
sect the curves. Horizontal lines taken from these points will 
intersect the vertical line g at the point indicating the mag- 
netization given by the magnetizing force indicated by the point 
of H oil which the vertical line was erected. 

Practical Considerations. — In the building of dynamos, the 
permeability of the iron used for cores of armatures and of field 
magnets has to be known. This knowledge is essential for the 
calculation of their construction. Without knowing the perme- 
abilities, the intensity of the field of force cannot be prede- 
termined. 



180 ELECTRICIANS' HANDY BOOK. 

The curves in Fig. 79 show that soft annealed iron gives the 
highest values of g for given values of p. It is evident from 
the curves that when a density of 16,000 lines of force is 
produced, it is not worth while to increase H, ^9 B ^i^l grow 
very slowly. But little will be gained by pushing H beyond 
10 or 20 for soft annealed iron. Energy is expended in the 
maintenance of the electromagnetic field of force, under the 
present conditions of electric construction. Whether this should 
be so or not is an open question, but the case is that the value 
of H is proportional to the energy expended on the field cir- 
cuit. It follows that where for a given value of H the highest 
value of B is reached, the best results are got for a given 
expenditure of energy on the field. The diagram shows that 
of the materials specified on the chart, soft annealed iron is best 
adapted for the production of an electromagnetic field. 

Glass-hardened steel sweeps upward across the diagram, show- 
ing no signs of approaching saturation. 

Any quantity of such diagrams could be produced. The one 
given illustrates their principle. The relation of B to H i^ 
most conveniently studied from such curve diagrams. Thus, 
if it is desired with annealed steel to produce a field of 8,000 
lines of force per square centimeter, the .diagram shows that a 
magnetizing f6rce sufficient to produce about 15 lines of force 
in air should be employed. 

As a matter of practice in dynamo construction and operation, 
B is generally in the neighborhood of 16,000. 

Q 

Permeability Curves,— We have seen that tt" which is never 
less than unity, or 1, is called permeability and is designated 
by the Greek letter u. B varies with H as we have seen, but 
not in direct proportion to it. Therefore, varies with dif- 

ferent samples of iron. This is because the relations of ' B to H 
vary with different irons. The curves shown on the next dia- 
gram, Fig. 80, show variations in permeability. The horizontal 
base line is divided for values of B- the existing field. The 

p 
vertical line, A, is divided for the values of the quotient of -rj- 

or ju. The curves show how ju , which indicates the perme- 



THE FIELD OF FORCE. 



ISl 



ability of different kinds of iron, varies as B' the magnetic 
field, is greater or less. 

The curve of permeability often rises at first. The greatest 
permeability in such a case is not at the lowest value of B. Thus. 
in one case for commercial wrought iron the permeability was 
found to be greatest when B. its A^x density or field, was equal 
to 6,000 lines of force per square centimeter of cross section. 



81 UO 
8000 
2800 


A 




\, 




















^ 


\^^, 


















\'k. 






















\V. 






















^ 
















-~~J^ 


^^n, 


^^ 


9-. 
















■ 


^ 


C/, 


\^^. 




















^^4^ 


\<P 




















\ 


x-^\ 


h- 












\ 








\^J 


\\ 












1- 


1 






^ 


i< 


\% 












< 


'>p> 








w 


fe 












\<i 








\ 


x\^fc 






400 






\^ 










X 










\ 


"^Hni 








X 


V. 















^//vso 


N) 






-^ 


^B 


P c 


\ 


1 1 


\ 


\ \ 


\ \ 


\ 


\ 


i 


I I 





Fig. 80.— Perme ability Curves. 



Soft Steel in Dynamos. — But these low flux densities have 
little interest from the practical standpoint. To economize in 
size and consequent expense, the field in electromagnetic ma- 
chinery is made strong by high excitation. Annealed mild steel 
above 13,000 lines of force flux density has much higher perme- 
ability than soft iron. Such steel, owing to the introduction of 
the open-hearth and Bessemer processes, is cheaply produced 
and is much used for field magnets. 

Annealfng.— The curves on both the diagrams show that an- 
nealing is of great value. The annealing should be done after 
all operations tending to harden the iron are over. 



182 ELECTRICIANS' HANDY BOOK. 

Determination of Curves.— The curves in this class of dia- 
grams represent the > result of measurements made by labora- 
tory processes. Thus in the laboratory a series of magnetizing 
forces are caused to produce a part of a magnetic circuit through 
a piece of the iron which is to be tested. The density of field 
produced by each magnetizing force is determined, and the two 
are entered in parallel columns. One column is headed H^ the 
other B. It may be that direct values of permeability are de- 
sired. Then a third column is added. Each value of B is divided 
by its corresponding value of H, and the result entered in 
the parallel ju or permeability column. 

Suppose in the experiments in the laboratory a magnetizing 
force of H=l-66 has been applied to a sample of annealed 
wrought iron, and has produced therein an excitation or mag- 
netic field represented by g = 5000. If we divide 5000 by 1.66, 
the result is 3000, or a := 3000. This gives us the figures for 
the top line of our three columns. Applying a magnetizing force 
of H = 4, we get B= 9000,' and dividing 9000 by 4 we get ju = 
2250. The process is repeated for different increasing values of 
B, and the results of such a series of tests are tabulated below. 





ANNEALED WROUGHT IRON. 




H 


B 


f^ 


1.66 


5,000 


3,000 


4 


9,000 


2,250 


5 


10,000 


2,000 


6.5 


11,000 


1,692 


8.5 


12,000 


1,412 


12 


13,000 


1,083 


17 


14,000 


823 


28.5 


15,000 


526 


50 


16,000 


820 


105 


17,000 


161 


200 


18,000 


90 


350 


19,000 


54 


666 


20,000 


• 30 



The three factors B, H, and /.i are as essential to the dynamo 
or motor builder as are the three factors of Ohm's law. 

I 



THE FIELD OF FORCE. 183 

Relation Between Ampere Turns and Lines of Force. — The 

field of force in practice as in dynamos is produced by ampere 
turns. If the current passing through the coils of an electro- 
magnet is multiplied by its convolutions, it gives the ampere 
turns. If the ampere turns are multiplied by 1.257, it gives 
the value of in gausses. Thus, to produce 10,000 lines of force 
in a pcth of air, 1 centimeter long and 1 centimeter square, 

10,000 

.= 7954 ampere turns will be required. 

1.257 

Leakage of Lines of Force. — As there is no insulator for lines 
of force, their escape from the path laid out for them is to be 
anticipated. A subma,rine cable will lose current if badly in- 
sulated, and a magnet core cannot be insulated as regards lines 
of force, because there is no insulator of magnetism, and hence 
its lines of force must leak. 

The iron used for magnet cores possesses several hundred 
times higher permeability than that of air, copper, or other ma- 
terial. The core of a field magnet therefore retains within itself 
a great proportion of the lines of force, but many leak across 
from one limb to the other. The perfect magnet would have no 
leakage, and the lines of force in undiminished numbers would 
issue from one pole and curve around through the air to the 
other pole. 

The leakage is greatest where the parts of the magnet core 
or other path of the greatest difference of polarity approach 
the closest. If the poles come close together, the air in their 
neighborhood will possess the greatest density of field and the 
leakage may be the greatest in their vicinity. An armature 
brought near the poles draws the lines of force into itself, modi- 
fying and reducing the leakage. 

The relative amount of leakage is expressed by a figure called 
the coefficient of leakage. This expresses the ratio of total field 
to useful field. The latter is composed of the lines of force 
which go through the armature. On dividing the total lines of 
force existing in the circuit by those going through the arma- 
ture, the coefficient of leakage is obtained. It varies from 
1.15 up to 2.00 or more. If the latter figure holds, it indicates 
a loss of one-half the excitation. The larger the electromagnet, 



184 



ELECTRICIANS' HANDY BOOK. 



the lower is the coefficient of magnetic leakage. In the large 
modern dynamo the leakage coefficient is very small. 

A high degree of magnetization decreases permeability. As 
the permeability grows less, the leakage increases. 

Stray Field. — The lines of force about a magnetic circuit can 
be divided into those which lie in the circuit and those which 
leak across it through the air or other substance. The lines of 
force which leak out of the circuit constitute what is called a 

stray field. The cut, Fig. 81, 
shows the stray field of the 
electro-magnet of a bipolar dy- 
namo with an iron base. 

Permeance of a flagnetic 
Circuit. — The permeance of 
the magnetic circuit of a dy- 
namo or like machine varies 
with the permeability of its 
constituent parts, with their 
cross-sectional area, and with 
tlie lengths of the different 
parts. The permeability of the 
iron of the magnet core must 
be known, and is in good prac- 
tice determined for each var- 
iety of iron used. The per- 
meability multiplied by the 
cross-sectional area of the core 
and divided by the core length 
gives the permeance of the magnet core. The permeance of the 
armature is obtained in like manner. The air-gap permeance is 
obtained in the same way, except that air has a permeability of 
1 always, so that unity is employed in the calculation for the air 
gaps where special permeability values were employed in the . 
other parts of the magnetic circuit. 

The reciprocals of the permeances or reluctances of the parts 
of the magnetic circuit thus determined are obtained by ex- 
pressing them as denominators of fractions with numerators 1. 
Thus, if the permeance of one part was 1000, its reluctance 




Fig. 81.— Lines or Force in Sp.ace 

Surrounding a Bipolar Dynamo ; 

THE Stray Field. 



THE FIELD OF FORCE. 185 

would be 1/1000. The reluctances are added together by the rule 
for addition of fractions, which gives the total reluctance. The 
reciprocal of this quantity gives the total permeance of the 
circuit. 

Hysteresis. — When a blacksmith puts a bar of iron in the fire 
of his forge, it takes some time for it to come to a welding 
heat. If a piece of iron is subjected suddenly to a magnetizing 
force, it takes a certain length of time for it to acquire the full 
effects of the force. Just as the hot bar cools slowly, so the iron 
which was made a magnet by magnetizing force loses all or a 
part of its magnetization when that force is annihilated, but a 
certain time is required for this. The two cases are exactly 
analogous to the action of heat. The delay in changing the state 
of magnetization is called hysteresis. 

If iron is subjected to an increasing magnetizing force, the 
magnetization will increase. Then if the magnetizing force be 
diminished, the magnetization will decrease, but not as rapidly 
as it increased for the same changes in H o^" magnetizing force. 
After the magnetizing force has been reduced to zero, the iron 
will retain more or less magnetization. To cause it to disappear 
completely, an opposite or reverse magnetizing force must be 
applied This will bring the magnetization to zero if the reverse 
magnetizing force is of the right degree of strength. Hysteresis 
is the tendency of magnetization to lag behind the magnetizing 
force. 

Residual flagnetism.— The magnetism retained by the iron 
after the magnetizing force has ceased is called residual mag- 
netism. It varies in amount with the quality of the iron. It 
tends generally to diminish with time, with changes in tem- 
perature, with other molecular and mechanical factors and ac- 
tions, so that its permanency is variable. 

Hysteresis is due to or is a phenomenon of residual magnetism. 
It therefore is of higher degree in steel than in soft iron, because 
steel retains more residual magnetism than soft iron does. 

Hysteresis Curves. — Its action is shown in hysteresis curves. 
In the diagram. Fig. 82, are given curves from Ewing, indicating 
the action of hysteresis in an annealed steel piano-forte wire. 
The horizontal lines of the diagram are divided for positive and 



186 



ELECTRICIANS' HANDY BOOK. 



negative values of the magnetizing force, |-|, from to 100 and 
to — 100. The vertical lines are divided for values of g from 
to 15,000 and to — 15,000. The magnetizing force H applied 
by degrees gave the values of g indicated by the curve starting 
from 0. Thus, for H =1^ we have B= about 1800, for H = 50 
B = nearly 12,000, and for H = 90 B = (a little more than) 
14,000. The magnetizing force was now reduced, when the left- 
hand curve gives the effects of residual magnetism. On the re- 
duction when H = B = (a little more than) 10,000, and this 
value of B== 10,000 is the residual magnetism. To reduce B to 




.—Hysteresis Curves. 



a demagnetizing force of H = (about) —23 is needed. On fur- 
ther applying minus values of \-{, opposite magnetism is in- 
duced in the steel until H = — 90 a value of about — 14,000 is 
reached for B, If now |-| is brought back to zero, B = (a little 
more than) — 10,000, just as before the positive values of B, 
end this again is permanent magnetism of opposite polarity to 
the preceding. As before, B becomes zero when H has the same 
numerical value as before, but of opposite sign, or H^=^ (about) 
20 when B = 0. On increasing m, the value B= (^ little more 
than) 1400 is reached when H ^^^ ^^^ ^^^ value of 90. 

The curves give an open figure; they inclose an area, and the 



THE FIELD OF FORGE. 187 

whole resembles an indicator diagram. Like the latter, it repre- 
sents a cycle which could be repeated indefinitely. 

Loss of Energy Due to Hysteresis. — The area is proportional 
to the energy converted by hysteresis into useless heat. 

The loss of hysteresis affects the operations of much electro- 
magnetic machinery and of alternating-current transformers. 

Hysteretic Constant.— A very simple formula for the loss has 
been produced by C. P. Steinmetz. Calling h the loss measured 
in ergs due to hysteresis per cubic centimeter of iron and for a 
single cycle, the formula reads as an equation: 

The Grreek letter 77 (eta) is a constant called the hysteretic 
constant. The equation holds good for a frequency of cycles 
of alternation up to 200 per second. This is twice that of stan- 
dard alternating current systems. Remembering that 10" ergs 
are equal to one watt or volt-ampere, we can at once see just 
what waste of energy there may be occasioned by hysteresis in 
any case. 

The hysteretic constants for various qualities of iron are 
given in the table. 

Very soft iron wire 0.002 

Most ordinary sheet iron 0.004 

Soft annealed cast steel 0.008 

Cast iron 0.016 

Hardened cast steel 0.025 

To get the loss in watts from the above, it is simply necessary 
to substitute the proper coefiicient for rf in the equation and 
divide by IQ-'', or what is the same thing, to multiply by 10-'. 
Suppose the material used had the coefficient 0.003. The watts 
loss would then be equal to 0.003 X 10-' X B^"^ X '^- The number 
of cycles indicated by n has to be introduced, because Steinmetz's 
original equation refers to a single cycle only. 

When a magnetizing force is applied without change to a piece 
of iron, its magnetization increases sometimes for half an hour 
or more, sometimes to the amount of several per cent of the 
magnetization. This is termed viscous hysteresis by Bwing, its 
discoverer, and sometimes it is termed magnetic creeping. 



CHAPTER IX. 

MAGNETS. 

The Electro=Magnet.— If a bar of iron is inserted in the axis 
of a coil of wire through which a current is passing, it will 
become magnetized and will attract iron. If free to move, one 
end, and always the same end, will point toward the north pole 
of the earth; not directly in that direction, except over a limited 
area of the earth's surface. Turning back to page 170, we see 
in Fig. 76 the diagram of a straight electro-magnet. The letter 
N indicates the north-seeking end of the pole, the letter S the 
south-seeking end. They are generally called the north and 
south poles of the magnet. 

Tractive Force of the EIectro=Magnet.— A piece of iron by 
presenting a good path for the lines of force in the vicinity of an 
excited electro-magnet virtually concentrates a number of them 
within itself. Other things being equal, a line of force tends to 
become as short as possible, acting something like an India-rubber 
band. Hence the lines extending from magnet face to armature 
tend to become as short as possible, and this tendency pulls the 
armature toward the magnet, just as if a multitude of India- 
rubber bands connected the two. 

Spreading of Lines of Force. — In air lines of force spread 
apart, which might seem to contradict the above. But the lines 
not only tend to shorten their paths, but do not easily change 
direction. A line starts out straight from the surfaces of a mag- 
net, and curves gradually toward the other surfaces. This ten- 
dency to start straight (normally) from a surface gives the 
lines of force a feather-like contour. 

Illustrating Lines of Force About a Hagnet. — The cut. Fig. 
83, shows the direction of lines of force about the north and 
south poles of a magnet, as shown by iron filings on a card or 



MAGNETS. 



189 



V 



■t 



ty\ 



slip of paper. All these effects shown by iron filings may be made 
to give permanent records by using a piece of blue print paper, 
such as employed by draughtsmen. The paper is placed over 
the poles in a horizontal position in a somewhat obscure place. 

The filings are dusted on the 

paper, which may be tapped or 
shaken a little. It is exposed to 
strong daylight or sunlight with 
the filings in place, and is then 
soaked in water, the filings first 
being removed. Very interest- 
ing prints can be made in this 
way. 

Spiral EIectro=nagnet.— If an 
active conductor is surrounded 
by a spiral of iron, as shown in 
Fig. 84, the spiral will become 
magnetized and will become a 
magnet, with poles at N and S. 
this connection. 

U=Shaped Electro=Magnets. — The horseshoe or U-shaped elec- 
tro-magnet is a type which has been very extensively used. The 
core represents a portion of a circle, three sides of a rectangle 
or some similar form, and generally two coils of wire are wound 



^-^K"^^.^_,i. 



Fig. 83.— Magnetic Lines of Force 
Shown bt Filings. 

Fig. 78 may be referred to in 




Fig. 84.— SpiBAii Electro-Magnet. 



upon two of its sides. The sides are called legs or limbs, the 
connecting portion of the core is the yoke. A typical magnet, 
such as used in telegraph instruments, is shown in Fig. 85. An- 
other wound with coned coils of wire is shown in Fig. 86. The 
wire is wound in opposite directions on the two legs of U- 
shaped magnets, as indicated in Fig. 87, in which arrows are 



190 



ELEGTRIGIAN8' HANDY BOOK. 



used to show the direction of the current around the core, whose 
poles, marked N and S, are supposed to face the observer. 

A powerful form is that proposed by Silvanus P. Thompson and 



ifm™^"?!^ 


1 i "" 


™''' ' ' "fi 


^llf 






— ^y' 


r. 




■:_-_H 


1 


1 


i^:',i ,i! 




iiii 


i|H 




iiir 







Fig. 85.— Typical Instrument 
Electro-Magnet. 




Fig. 86.— Electro-Magnet with Coned 
Coils. 



shown in Fig. 88. A thick, short magnetic circuit is provided by 
the core of this shape. 

The magnetic circle, Fig. 89, is very similar, and shows how a 
U-shaped magnet can be excited by a single coil. This form is 
made for lecture purposes about three-quarters inch thick, bent 





Fig. ST.— Winding of a TJ-Shaped 

EleOTRO-M AGN ET. 



Fig. 88.— S. p. Thompson's 
Electro-Magnet. 



into half circles of about two inches internal diameter. It is 
exceedingly powerful, presenting a path of high permeance for 
the lines of force. 

Joule's electro-magnet, Fig. 90, is a very old form, and one 
which has given very high tractive power. It was one of a num- 



MAGNETS. 



191 




Fig. 89.— Magnetic Circle. 



ber of forms of electro-mag- 
net devised by- J. P. Joule in 
the first half of the last cen- 
tury. The volt-coulomb or 
joule is named in honor of 
this distinguished scientist. 

The hinged electro-magnet. 
Fig. 91, needs no armature. 
When a current is sent 
through its coils, the two legs 
swing together and their ends 
touch each other. 

An example of a U-shaped 
magnet with a single coil is 
seen in Fig. 92. This type is 
called by the Germans a limp- 
ing magnet, which S. P. 
Thompson renders club-foot. 
A pivoted armature is pro- 
vided for these particular 
magnets. 

Annular Chambered Hagnet-A number of electro-magnets 
whose exciting coils are contained in annular chambers or grooves 
have been devised. One used for lecture experiments is shown 

in Fig. 93. It may be 
called the electro-mag- 
netic Magdeburg hemi- 
speres. The magnet 
and armature are indi- 
cated by ao. and are 
identical. The section 
of one. A, is shown 
with the exciting coil 
C. The iron-jacketed 
electro-magnet. Fig. 94, 
is practically one part 
of the above device, and is intended to attract a flat armature. 
A practicar application of this type is shown in the electro- 




FiG. 90.— Joule's Electro-Magnet. 



192 



ELECTRICIANS' HANDY BOOK. 



magnetic clutch. Fig. 95. Brushes B B bear upon insulated rings 
CC on the hub of a band wheel, which is free to rotate on a 
shaft. Current entering by the brushes excites the annular coil, 
which magnetizes the band wheel and draws it against the disk 

A A. The latter is keyed to the 
shaft and rotates with it. When 

^ — I I CTV. V *^® ^^^^^ ^^^ ^^^® ^^^^ wheel are 

Xj^^^^^^^^^^^^^^ drawn together, the wheel has 

^i^^^^^^^y /^^ to turn with the shaft. 

Electro = flagnetic Tractive 
Power.— A pair of wheels may 
be drawn together by a coil, as 
is shown in Fig. 96, thus one 
wheel being caused to grip or 
press against another, so as to turn it. The arrangement shown 
is of very limited application, and owing to the poor magnetic 
circuit, is far from efficient. A better arrangement is shown in 
Fig. 97, where a current of electricity passed through a coil car- 




FiG. 91.— Hinged Electro-Magnet. 





Fig. 92.—" Club-Foot " or Limping Electro- 
Magnets. 



ried by a car wheel increases its traction on a rail. The coil is 
annular and lies in the groove around the wheel. The current 
enters by brushes, as in the clutch just illustrated. 

'Multipolar Hagnets are shown in two examples — Joule's "zig- 
zag," Fig. 98, and Roberts', Fig. 99, electro-magnets. These, in the 
light of what has been said, explain themselves. In them the 



MAGNETS. 



19S 



usual letters N and S indicate north and south poles, and the 
arrows indicate the direction of the current. 

Various Armatures. — Cam mechanism due to Robert Houdin, 
the famous French magician, is shown in Fig. 100. E is the 
electro-magnet attracting its armature a. The cam A acts upon 
B. By varying the shapes of the faces of the cams, all sorts of 
results in the motion of the distant rod can be reached. 

The armature shown in Fig. 101 
is attracted upward from the posi- 
tion shown in the dotted lines when 
the magnet is excited. It also 
presses against the drum, which is 
part of the core, and rotates it so 
as to turn the gear wheel on the 
further end of the shaft. A spiral 
spring may pull upon the short arm 
to draw the armature back. This 
operates like a ratchet and pawl 




,^lIiE^ 




Fig. 93.— ANNiTiiAR Chamber- 
ed Electro-Magnet. 



Fig. 94.— Iron-Jacketed 
Electeo-Magnet. 



mechanism, as it only operates to turn upon its up-stroke. 

In this magnet the core must be free to turn in the coil. In 
Fig. 102 is shown another magnet with rotating core. A is the 
rotating core, turned in one way by the pull upon the armature 
projecting from its lower end. The arm D is of brass, C is of 
iron. The core B is fixed. 

Other pivoted armatures are shown in the cuts. Figs. 103 and 
104. 



194 



ELECTRICIANS' HANDY BOOK. 



I 



The Natural Magnet is a mineral consisting of a combination 
of iron and oxygen, whose composition is indicated by the chem- 
ical formula, Fe304. The mineral is called magnetite, and is char- 
acterized by being attracted by the magnet just as iron is, only 
not so powerfully. Some samples of magnetite do more than 
this, as they attract iron themselves. Such are natural magnets, 
known to the ancients as the lodestone. The attractiveness for 
iron is localized in each piece, being at a maximum at certain 





Fig. 95. -Electro-Magnetic Clutch. 



Fig. 96.— Electro- Magnetic 
Drive. 



points. These points act upon the compass needle, each repelling 
one end of it and attracting the other end. If the mineral were 
suspended by a delicate enough pivoting or suspension, one of the 
attracting points on it would seek the north pole. 

The Permanent Magnet is a piece of steel which has been 
charged with magnetism, and which retains it. It attracts iron, 
its ends doing so most strongly; tends to point north and south, 
the same end always tending to the same pole; and thus de- 
termines what are generally called its north and south poles. 
Sometimes they are called the north-seeking and south-seeking 
poles. 



MAGNETS. 



195 



Action of riagnet Poles on Each Other* — The north poles of 
two magnets tend to repel each other, and the south poles repel 
each other exactly the same. A north pole of one magnet attracts 
the south pole of another. Like repels like, and unlike attracts 
unlike. Magnets repel each other just as much as they attract 
each other. 

Making Magnets by Single Touch.— One process of making a 
magnet is shown in Fig. 105. A bar of steel lying on a table is 
stroked from center to end with one pole of a permanent magnet, 
the arrow showing the motion. The stroking magnet is returned 
through the air to the center of the steel bar, and a second stroke 




ho. 97,— Electro-Mag- 
netic Cab Wheel. 



Fig. 98.— Joule's Zigzag 
Electbo-Magnet. 



Fig. 99.— Roberts' 
Electro-Magnet. 



is given. This is repeated a number of times, and then the same 
operation is gone through with the other pole of the magnet on 
the other half of the bar. The end of the bar stroked with the 
north pole of the magnet will be a south pole and vice versa, 
as indicated by the letters N, N and S, S in the cut. This process 
is called single touch. The stroking may be done for both halves 
with two magnets simultaneously, as described above for one. 
The north pole of one magnet and the south pole of the other are 
brought together or nearly so on the center of the bar, and simul- 
taneously moved out along it, are swept back to the center through 
the air, and the stroking is repeated. A little bit of wood may 
be placed across the center of the bar to keep the magnets from 
touching each other at the beginning of the stroke. 



196 



ELECTRICIANS' HANDY BOOK. 



Making flagnets by Double Touch.— For this the opposite poles 
of two magnets are brought close together, separated by a slip 
of wood or pasteboard, the magnets being inclined at an angle of 
over 90° to each other, like a V with very wide angle. Fig. 106. 
The apex is placed on the center of the bar, and is moved ten to 
twenty times slowly back and forth over the whole length of 
the bar. 

In both single and double touch the effect is increased by rest- 
ing the ends of the bar to be magnetized upon the opposite poles 




I 



Fig. 100.— Cam Mechanism fob Electro- Magnets. 

of two other magnets. The poles must be the same as those 
of the magnet with which the stroking of the end in question is 
done. 

flaking U-Shaped Magnets. — This type of magnet is universal- 
ly called a horseshoe magnet. A bar of iron of this shape may 
be magnetized by stroking with another horseshoe magnet, from 
near the bend to the ends, or from ends to the bend. As for 
straight magnets, the magnet must be returned through the air. 
A piece of iron should be laid across the ends during the process. 
An excellent way of magnetizing U-shaped bars used for volt- 
meter magnets is to place the ends of the bar against the two 



MAGNETS. 



197 



poles of a powerful electro-magnet. Each end touches its own 
pole, and the adherence is strong. The operative now rocks it 
back and forth a number of times as it adheres to the electro- 
magnet, thus slightly jarring it and causing it to become per- 
manently magnetized. 

Magnetizing by Coil and EIectro=Magnet.— A compactly-wound 
coil of wire was proposed by Elias of Haarlem for making mag- 
nets. Through such a coil a current was passed, and the coil 
was moved from end to end of the bar to be magnetized. The 
coil may be slid thus over a U-shaped bar while its ends are in 





Fig. 101.— Calombet's Electro- 
magnetic Pawl.. 



Fig 102.— Waterhofse'i 
Pivoted Armature. 



contact with a powerful electro-magnet. A successive turning 
on and off of the current of the electro-magnet is used sometimes. 
Another suggestion was to apply the steel bars while red hot to 
the poles of an electro-magnet, and to pour cold water on them 
while there. 

Steel for Magnets. — Tungsten steel is considered the best ma- 
terial for permanent magnets. Hopkinson gives the analysis of 
such a steel: 

Iron 95.371 

Carbon 0.511 

Manganese 0.62^ 

Silicon 0.021 

Phosphorus 0.028 

Tungsten 3.444 



198 ELECTRICIANS' HANDY BOOK. 

Chrome steel containing 0.687 carbon and 1.195 chromium and 
no tungsten also gave Hopkinson good results. 

Preservation of flagnets. — Jarring should be scrupulously 
avoided. The armature of a magnet should not be allowed to 
come against the magnet violently. It should be gently put 
into place. Jerkii^g the armature off does no harm unless a 
positive jar or clicking is produced. A horseshoe magnet should 
have its armature in place when it is put away, and bar magnets 
should be in pairs, with poles in reverse direction and connected 
by short bars or armatures. 

Examples of Permanent flagnets— A compound U-shaped 
magnet is shown in Fig. 107. The body is made of thin bars 





Fig. 103.— Oscillating Fig. 104.— Siemens's Pivoted 

Armature. Armature. 

supposed to be magnetized separately, and then fastened to- 
gether. An iron armature a with a hole serves to show its lift- 
ing power. Weights are attached by means of the hole. The 
above would often be termed a horseshoe magnet. A true horse- 
shoe magnet is shown in Fig. 108. There the poles are very 
close together. Such a magnet can be used for magnetization 
by double touch, on account of the proximity of the poles. 

An iron bar with a wheel of lead or brass mounted on its 
center and placed across the legs of a magnet, as shown in Fig. 
109, will if it is inclined roll down the magnet around the poles 
and up the under side of it, actuated by the momentum of the 
little flywheel. In the next cut. Fig. 110, little bars of iron with 
disks at the ends are placed together, as at A. On bringing a 
magnet above them, they become similarly magnetized, and as 



MAGNETS. 



199 



they lie with north pole to north pole and south pole to south 
pole, they are driven apart by mutual repulsion, indicated by 
B, B. 
Polarized and ilagnetized. — When magnetism is spoken of, 




Fig. 105.— Making a Magnet by Single Touch. 

these words are synonyms. A polarized piece of steel is a mag- 
netized one. A polarized relay in telegraphy is one whose action 
depends upon a permanently magnetized armature. 

Constancy of flagnetisnio — For instruments such as volt- 
meters, the critical thing is to have magnets of great constancy. 




Fig. 106.— Making a Magneo? by Double Touch. 

To secure these, they must not be too strongly saturated, as such 
a procedure produces magnets which lose readily part of their 
strength. 

nutual Action of Currents.— Two parallel conductors through 

which currents are passing attract each other if the currents 

are flowing in the same direction. If one current is flowing in 

j one direction and the other current in the reverse direction, the 

conductors repel each other, 

I 



200 



ELECTRICIANS' HANDY BOOK. 



Ampere's Theory of riagnetism.— Based on the above facts 
and on the construction of the electro-magnet, the celebrated 
Ampere's theory of magnetism has been formulated. It ac- 
counts for the mutual attraction and repulsion of magnets, and 
for their tendency to place themselves in the magnetic meridian 
and to have one end seek the north pole. 

A current of electricity is assumed to circulate around each 
molecule of a magnet. The cut, Fig. Ill, shows the theory. It 






Fig. 107.— Compound 
U-Shaped Magnet. 



Fig. 108.— Horses 
Magnet. 



Fig. 109.— Magnet with 
FLYWHEEii Armature. 



will be seen that the effect is as if a single current circulated 
around the outside of the magnet. The parts of the currents ad- 
jacent to each other in the interior counteract each other, and 
the outside currents virtually coalesce into one. This is the con- 
ception of a magnet according to Ampere's theory. 

It will be seen that the current denoted by the outside ar* 
rows corresponds to the current through the windings of an 
electro-magnet. If the observer faces the north pole, the Amper- 
ean current, as it is called, will circulate in direction opposite to 
the motion of the hands of a watch. If we face the south pole. 



MAGNETS. 



201 



the current will coincide in direction with, the motion of the 
hands of a watch. 

Memoria Technica,— A watch indicates seconds, and could prop- 
erly have the letter S marked upon its glass. It would then rep- 
resent the south pole of a magnet, its hands in their motion giv- 
ing the direction of the Amperean currents. The watch has 
been used before to fix on the mind the relation between an elec- 
tric current and its lines of force. The "S" may be taken as the 
symbol for "seconds" and "south pole." 

Taking the face of a watch as indicating the south pole of a 





Fig. 110.— Rolling Armatures. 



Fig. 111.— Ampere's Theort of 
Magnetism. 



magnet, it tells us how the lines of force go. As the watch tells 
us that time flies from us, it tells us that at the south pole the 
lines of force fly from us. They issue from the north pole and 
return to the south pole through the outer circuit. 

Ampere's Theory of Terrestrial Magnetism.— A magnet points 
north and south, approximately, the same pole always pointing 
north. By Ampere's theory this is accounted for by supposing 
the earth to be a great magnet, and to be encircled by currents 
flowing around it, approximately parallel to the equator. 

If currents of like direction attract each other, then if placed 
at an angle with each other they will tend to coincide in direc- 
tion. Currents tend to become parallel with each other, and to 



202 



ELECTRICIANS' HANDY BOOK. 



coincide in direction also. If two conductors are free to rotate, 
and currents are passed through, them, they will tend to rotate 
like a compass needle until parallel with one another, with the 
current flowing in the same direction in each. 

The theoretical ampere currents of the earth force the ampere 
currents which are supposed to encircle a magnet into parallel- 
ism and similar direction, and thus cause the compass needle to 
point to the north. 

Attraction and Repulsion of flagnetic Poles.— In Fig. 112 are 
shown two pairs of magnets. One pair has its north pole facing 
the south pole of its neighbor. The arrowheads indicate the 
direction of the Amperean currents. The currents in both poles 




Fig. 112. 



-Ampere's Theory Explaining Attractive and 
Repulsive Forces Between Magnets. 



correspond in direction, and as currents of like direction attract 
each other, the north pole of the magnet S N and the south pole 
of the magnet Si Ni attract each other. 

This refers to the upper pair. In the lower pair one magnet 
has been turned end for end. The Amperean currents are now 
opposite in direction, and the north poles of the magnets SN and 
Ni Si repel each other. 

If the south poles were brought together, repulsion would also 
exist, because the Amperean currents would again be opposite in 
direction. 

Action of a Current on the flagnet. — A compass needle in 
the vicinity of an electric current is acted on by it, and tends 
to place itself at right angles thereto. It never can unless the 
current is at right angles to the magnetic meridian, but the 



MAGNETS. 203 

tendency is present. Thus a current deflects a compass needle, 
if the compass is held near the conductor/ unless the conductor 
is at right angles to the magnetic meridian, or lies nearly or 
quite east and west. 

Remembering that the magnetic needle of the compass is sup- 
posed to have Ampere currents circulating around it in planes at 
right angles to its axis, this directive tendency of the compass 
needle will be recognized as an effort of the Ampere currents to 
place themselves in parallelism with the current in the conduc- 
tor. If held above the conductor, the needle will be deflected in 
one direction; if held below, it will be deflected in the other. 
Ampere has devised a rule for remembering the ways in which a 
magnetic needle will be acted on by a current in a conductor 
near to it. 

Ampere's Rule. — If a man were swimming with the current 
in the conductor and had his face turned toward the magnetic 
needle, its north pole would be deflected toward his left hand. 
This means that if the needle was above the conductor, he would 
have to be on his back to face the needle; if it was below, he 
would have to be on his face. Hence the needle will turn in 
reverse ways according to whether it is above or below the con- 
ductor. 

If the direction of the Ampere currents be formulated in the 
mind, it will be seen that the above deflection of the magnets 
simply brings them in parallelism with and coincident in direc- 
tion as regards their nearest portion with the current in the 
conductor. 

A coil of wire traversed by a current represents a magnet. In 
physical experimenting, such coils called solenoids are used to 
illustrate the Ampere law. They will, when passing a current, 
tend to point toward the magnetic pole; their unlike poles will 
repel each other; and they will act exactly as magnets do. If an 
inert bar of iron is surrounded by a conductor carrying a cur- 
rent. Ampere's law will be exemplified, and we will have an elec- 
tro-magnet. 

An electro-magnet is a bar of iron around which a current of 
electricity is caused to flow, so as to represent the Ampere mag- 
netizing currents of the permanent magnet. As we can make 



204 



ELECTRICIANS' HANDY BOOK. 




the artificial currents very strong, and give them as many turns 
around the iron (called a core) as we wish, 
an electro-magnet can be made very strong, 
many times stronger than the best perma- . 
nent magnet of equal weight. 

Right=handed Screw Law. — The relation 
of north and south pole to the current 
circulating around a magnet core is ex- 
pressed by the right-handed screw law. It 
is to this effect: 

A right-handed screw, such as a corkscrew. 
Fig. 113, placed so as to coincide with the 
axis of the magnet and turned in the di- 
rection of the current, will move toward the 
north pole of the magnet. The arrows 
and polar letters N and S in the cut indicate 
the relations. This is merely another state- 
ment of the watch law. 

Assuming the arrows to indicate the di- 
rection of current circulating around an - 
iron bar S N, it will be seen that if the end N 
were pointed at the reader, the current would be against the 
motion of the hands of a watch. The end pointing thus should 
be and is the north pole. If the corkscrew were turned in the 
reverse direction, its motion would indicate a current in the oppo- 
site direction to that shown by the arrows. If the lower end 
were pointed at the reader as before, the current would coincide 
in direction with that of the hands of a clock or watch, and the 
pole would be a south pole. 

Again, imagine a corkscrew pointed at the face and turned. 
If turned right-handedly, it would advance if the screw had a 
grip on anything. Its direction of turning would give the polarity 
of the lines of force due to a current moving in the direction of 
the observer. The reverse also holds. Both these statements 
express the watch-face rule for lines of force due to currents. 



Fig. 113.-CORKSCREW 

Analogy of the 

Magnet. 



CHAPTER X. 

INDUCTION. 

EIectro= Magnetic Induction. — If an electric conductor lies in 
a field of force, it may be in the vicinity of a magnet pole, it will 
be unaffected by the field, as far as any electromotive force in 
it is concerned. If the conductor is moved so as to cut the lines 
of force, or if the magnet is moved while the conductor is sta- 
tionary, which brings about the same result of cutting lines of 
force, electromotive force will be impressed upon it. There are 
many variations in the relations of conductors and fields of force 
which have the effect of impressing electromotive force upon 
such conductors, and producing currents in them if they form or 
are part of a closed circuit. In general terms the inductive effects 
summarized above involve attraction or repulsion between pole 
and conductor. 

Threading, Interlinking, and Cutting Lines of Force.— There 
are two general ways of taking cognizance of the action of a field 
on a moving conductor. It may be referred to cutting of lines 
of force by the conductor, or to changing the number of lines 
of force which pass through the space included in the electric 
circuit. The latter may be looked upon as a ring, or irregular 
circle-like lead of wire. The passing of lines of force through 
this circle of wire is often called threading or interlinking of 
lines of force. The latter expression is correct because lines of 
force form closed circuits of their own. 

Induction. — When an electric conductor forming part of a cir- 
cuit is swept through a field of force an electromotive force is 
impressed upon it. If the ends of the conductor were connected 
to a proper instrument, such as a voltmeter, the electromotive force 
would affect its index, and it would be evident that electromotive 
force actually existed. The cutting of lines of force by an electric 



206 



ELECTRICIANS' HANDY BOOK. 



conductor represents the impressing of force upon or transfer- 
ring of force to the conductor. The term force as last used 
applies to electromotive force. If the proper conditions are estab- 
lished the electromotive force impressed on the conductor by the 
field of force will produce a current. If these conditions do not 
exist no current will be produced. Thus there are two varieties 
of induction. In the one case energy in the form of volt-coulombs, 
or other electromotive force-quantity unit, is developed, and by 
the law of the conservation of energy the motion of the conduc- 
tor through the field of force is resisted, so that energy has to 
be expended upon it to move it across the lines of force. In the 
other case no current is produced and no energy is required to 
move an open-circuit conductor through the field. 






« 






< — ^^^^r=^ 


=^/^\ — — 


gg n 


" — \r4 


=¥=^F= 


^ — ^ 


— ^^ — ■ 


<= -* 



Fig. II4.—R1NG Moving in Field op Force 
Without Cutting Lines op Force. 

Conditions for Inducing Electric Energy.— The conditions for 
thus producing current are two. The conductor must form part 
of a closed circuit, and the number of lines of force passing 
through the loop or opening of the circuit must vary in number; 
or a portion of the circuit must cut lines of force. In most cases 
of dynamo generators both the latter conditions exist at once. 
As the armature conductors cut lines of force they vary the num- 
ber of lines of force interlinked with the circuit. 

Examples of Interlinking. — Assume a uniform field of force 
and let a ring of conducting material be moved in it. The cuts, 
Figs. 114 to 117, illustrate several conditions, the motion of the 
ring being indicated by the arrows. 



INDUCTION, 



207 



In the case illustrated by Fig. 114 the ring is swept through the 
field of force but cuts no line of force as its motion is parallel to 
them. Therefore no electromotive force is impressed upon it. 
In the case shown in the next cut, Fig. 115, lines of force are 
cut, therefore electromotive force is impressed; but as the num- 
ber of lines of force embraced in the ring is unchanging, no 
current is produced. Each half of the ring has electromotive 
force of the same polarity impressed on it and the two oppose 
each other, so that no current results. In Fig. 116 the ring is 
swung around so that it not only cuts lines of force, but the 
number of lines embraced by it is constantly varying, hence 



y 



r 



Fig. 115.— Ring Moving in Field of Fobck 

Cutting Lines of Force Withotjt 

Change of Interlinked Lines. 



electromotive force and current both result. In the next cut, 
Fig. 117, the ring is swept in a straight line through a non- 
uniform field of force. It not only cuts lines of force, but the 
number passing through it varies constantly. Electromotive 
force and current both are produced. In the first two cases no 
power is expended on moving the ring through the field; in the 
last two power is so expended. 

Motionless Conductor in a Field of Force of Varying Den= 
sity. — Where a ring or convolution of wire or other conductor is 
placed in a magnetic field, lines of force will pass through it, 
if its plane of position is at an angle to the general direction of 
the lines of force. Lines of force would be said to thread through 



208 



ELECTRICIANS' HANDY BOOK. 



it, but would have no effect whatever upon it. We have seen that 
a current would flow through it, actuated by electromotive force. 



^~ 


/i^^^ ^^\\^^> 




*"■ 


//Vi ^ 








^^ 






^, 






''x 




\V // 


-I 


< vs^ 


"^ 




/,^?«\ ' 






<^ )). 


^: // ^y 




\ 


^^^-^^i^x^ 


« — 



Fig. 116.— Ring Moving in Uniform Field of Fobcb 
Under Conditions Producing a Current. 

if the wire were moved so as to vary the number of lines of force 
embraced by the circuit. Suppose the wire or conductor to be 




Fig. 117.— Ring Moving in Field op Force 
Under Conditions Producing a Current. 

kept motionless and the density of the field of force to vary. This 
would cause the lines of force embraced by the circuit to vary 



INDUCTION. 209 

in number. Electromotive force and current would be produced 
in the conductor exactly as if it were moved. 

Energy Relations.— Energy would be absorbed whether the 
field of force was increased or diminished in density under the 
above conditions. The presence of the closed circuit would be the 
cause of such expenditure. It would by counter-electromotive 
force resist any change of field density which would produce 
energy in its conductor, and exact the expenditure of additional 

energy. . . ^ .^^ 

Fields of Force In Practice.— In practical engineering fields 
of force are produced by magnets, which are generally electro- 
magnets. They vary in the number of their poles, but follow . 
pretty closely some general rules. The poles are nearly always of 
even number; for every north pole there is a south pole; the 
north and south poles are placed in alternation with each other. 
Fields of force may be moved past conductors or past coils form- 
ing parts of circuits; or the conductors and coils may be moved 
past them- or the relations of field to conductors or coils may be 
kept changing, as in inductor generators. In all such cases elec- 
tromotive force is impressed on the circuits. The conductors or 
coils which are thus treated form part of armatures, and consti- 
tute the active portions of the armature windings. The effect of 
the processes is to cause the number of lines of force interlinked 
with the circuit to vary. A variation of 10« lines of force per 
second produces an electromotive force of one volt. 

Direction of Current Induced by Cutting Lines of Force.- 
If the north pole of a horizontally placed magnet face the ob- 
server the lines of force will come out of it toward him, will 
curve around and pass through the space surrounding the pole 
away from it to the south pole. If a perpendicular conductor is 
swept from left to right across the north pole an electromotive 
force will be induced in it, tending to produce in it a /^^rrent 
from above downward. Let a letter N be marked upon the pole. 
Rule lines upon the end parallel to the ^^^''^ZT vfZn^.i 
Cut a narrow slit in a card and holding it with the slit vertical 
move it to right or to left. The lines will appear through the 
slit like a series of dots, and will appear to move ^P.^^^^/;^ 
up for a motion to the left, down for a motion to the right. Their 



210 



ELECTRICIANS' HANDY BOOK. 



apparent motions indicate the direction of currents induced in a 
vertical conductor moved across the north pole, to left or to right. 
For the south pole the directions are the reverse. 

The cut, Fig. 118, illustrates the principle. In it the south poles 
are diagonally shaded in the opposite sense to the north pole. 
The same process of using a slotted card will show the direction 
of currents in a conductor swept across them. 

In the cut the arrows a h and c d indicate the direction of cur- 
rent induced hy motion in the direction of the dotted arrows. 
With motion in the other direction the currents would have the 
reverse directions. 

Two Systems of Induction. — Electro-magnetic induction can be 
referred to two causes. One cause is the cutting of lines of force 




Fig. 118.— Directions of Induced Currents. 



by conductors. This generally, as far as effective, has the result 
of changing the number of lines of force threading the circuit. 
The other way is to directly change the number of lines of force 
threading the circuit, without reference to cutting them by con- 
ductors. 

The first cause is represented by the conductors on a drum 
armature, one of which is indicated in diagram in Fig. 119; the 
second is represented by a type of generator in which coils whose 
planes are parallel to those of the field magnet coils are swept 
past the poles. Fig. 120. In the first case the electromotive force 
is at a maximum for any conductor when it is directly opposite 
the pole; in the second case it is at a maximum when the arma- 
ture coil is midway between two poles. 

Generator Without Motion. — We are accustomed to think of 



INDUCTION. 



211 



a dynamo or electric, generator as a machine in rapid motion 
when active, and inert when at rest. But from what has been 
said it follows that it would be perfectly practicable to have a 




Fig. 119.— Closed Loop in a Bipolar Field. 



dynamo without any moving parts if some way could be devised 
to change rapidly the intensity of the current passing through its 
field. A close analogue to such a dynamo is the alternating- 
current transformer. In it is a field 
of rapidly varying density with a 
conductor placed so as to have the 
lines of force pass through it. The 
changes in number of lines of force 
passing through it develop pulses of 
electromotive force so that an alter- 
nating current is produced. 

Examples of Induction. — If a tele- 
graph wire or trolley wire were 
carrying a steady current and were 
set swinging by the wind, it would 
carry with it its field of force which 
would swing back and forth some- 
thing like a huge cable. Theoretical- 
ly there would be no limit to its di- 
ameter, but its 'intenser field would be 
within a limited radius from the conductor as an axis. This field 
swinging back and forth would sweep its lines of force across any 




Fig. 120.— Bobbin Field and 
Disk Armature Coils. 



212 ELECTRICIAN IS' HANDY BOOK. 

contiguous conductor, and if the ends of the latter were con- 
nected to each other or to the ground, would cause currents of 
brief duration to flow back and forth through it. Thus the trol- 
ley wire's every swing, however slight, produces some current 
through the rails below it. 

The varying currents in a telegraph wire as Morse signals are 
sent through it make varying fields of force and set up pulses of 
electromotive force with consequent currents in contiguous con- 
ductors. The interference of telegraph signals with telephone 
circuits is a very familiar instance. 

Telephone Receiver a Dynamo. — The telephone receiver can be 
used as a transmitter and originally was used as such. The 
minute vibrations of the thin plate which is supported close to 
the pole of a permanent magnet make the lines of force move 
about a little so that the coil of wire surrounding the end of the 
magnet is cut by varying numbers of lines of force. These varia- 
tions induce electromotive force and currents, which reproduce 
in a distant telephone receiver the sounds of the voice. The 
telephone receiver used thus is really a dynamo. In actual tele- 
phone practice the microphone is used as a transmitter and induc- 
tion does not play any direct part in its functions. 

Laws of Induction. — There are several laws affecting electro- 
magnetic induction which may be given here. 

Faraday's Law is based on his discoveries in the induction of 
currents by the cutting of lines of force. It is given in the follow- 
ing words: 

"When a conductor is moved in a magnetic field so as to cut 
the lines of force, there is an electromotive force impressed on 
the conductor, in a direction at right angles to the direction of 
the motion, and at right angles also to the direction of the lines 
of force." 

Fleming's Rule for remembering this law and the connection 
between the three factors motion, magnetism, and induced elec- 
tromotive force is this: Hold the thumb and first finger of the 
right hand at right angles to each other. Let the forefinger rep- 
resent the lines of force and point in their direction. Then the 
hand will represent the north pole of a magnet. The thumb 
will represent the direction of movement of a conductor. The 



INDUCTION. 



213 



latter is represented by the middle finger pointing at right angles 
to the other two. Then moving the conductor in the direction of 
the thumb, an electromotive force in the direction in which the 
finger points will be impressed upon it. 

The words "current induced" may be substituted for "electro- 
motive force impressed." When direction is attributed to electro- 
motive force it refers to the direction of current which such elec- 
tromotive force would produce. 

The cut. Fig. 121, shows the relations of the three factors as 
described. 

Ampere's Rule Adapted to Induction. — Suppose a man swim- 
ming along a conductor with 
his back to the north pole of a 
magnet whence lines of force is- 
sue. Then if he and the conduc- 
tor together be moved toward his 
right hand, the induced current 
will flow in the direction in which 
he is swimming. 

When the movement is not at 
right angles to the lines of force 
a certain proportion of the move- 
ment can be found which will be 
at right angles and this represents 

the effective portion of the movement. The object of the adop- 
tion of the idea of perpendicular movement is for the sake "of 
simplicity. 

Clerk riaxweirs Rule. — If a magnet is in the presence of an 
active circuit which therefore produces a field of force, each por- 
tion of the circuit acts upon the magnet in such a direction as 
would cause the magnet, were it free to move, to take up the posi- 
tion in which the greatest possible number of its lines of force 
would be embraced by the circuit. 

Lenz's Law is a most convenient statement of the relations be- 
tween the motions of magnetic poles and currents induced by 
their lines of force. While such relations can be worked out 
from a lower basis, the summarization known as Lenz's law will 
be found an admirable tool to work with. It is all-essential to 




Fig. 121.— Fleming's Rule. 



214 ELECTRICIANS' HANDY BOOK. 

understand that it is in strict accord with Ampere's law. It is 
generalized by Daniell, author of "Daniell's Physics," thus: "When- 
ever a closed circuit capable of bearing an electric current lies 
wholly or in part in a magnetic or electro-magnetic field of force, 
any disturbance in the intensity of the field of force will induce 
a current in the circuit; and the direction of the induced current 
is determined by the rule that the new current will increase the 
already existing resistances (not electrical but mechanical resist- 
ance), or develop new resistance to that disturbance of the field 
which is the cause of induction." 

The law is more briefly expressed thus: When a conductor is 
moving in a magnetic field a current is induced in the conductor 
in such a direction as by its mechanical action to oppose the 
motion. 

It is also divided into two divisions, one for a generator read- 
ing thus: The induced current is always such that by virtue of 
its electro-magnetic effect it tends to stop the motion that gen- 
erated it. 

In accordance with this statement a dynamo requires more 
energy to be expended on it when it is generating current than 
when idle, because the passage of the current increases all elec- 
tro-magnetic effects and also the Lenz effect of resistance to 
motion generating the effects. 

For motors the converse division of the law is put thus: The 
motion produced in a motor by the passage of an electric current 
is always such that by virtue of the electro-magnetic inductions 
which it sets up it tends to stop the current. 

This division covers the case of counter electromotive force. 

Examples of the Application of Lenz's Law.— Synchronous 
alternating-current motors are addicted to varying in speed, going 
at one instant faster than the generator and at the next instant 
going slower. This action, disastrous to all regularity, is some- 
times called hunting. It is checked by inserting coils of wire or 
other conductors in the field magnet pole faces. Currents are 
induced in these by change of velocity of the rotations. By 
Lenz's law such induced currents tend to stop the objectionable 
hunting motion which produced them. 

A direct-current motor not doing anything and running with- 



INDUCTION. 215 

out any mechanical resistance ought, it would seem, to run at an 
indefinite and almost unlimited speed. As the motor turns it in- 
duces electro-magnetic effects, which are greater the faster it re- 
volves. By Lenz's law these effects are such as to oppose its mo- 
tion. As they increase with its speed, opposition to its motion 
increases with its speed. It cannot, therefore, exceed a certain 
rate. 

This is another way of stating the action of counter electro- 
motive force upon a motor. 

Complaint is sometimes made that electric cars go too fast in 
cities. Their speed could be easily limited by constructing their 
motors so as to have any desired limit of velocity of rotation. 

Two conductors carrying current in the same direction attract 
each other; in opposite directions, repel each other. If one wire 
is carrying no current but has its ends connected and the current 
through the other is increased, an opposite current will be in- 
duced in the second wire. The wires repel each other when cur- 
rent is induced, and in the opposite case, when induction is dimin- 
ished, attract each other. Lenz's law fails to touch this case be^ 
cause there is no mechanical motion. But let a steady current 
pass through one wire and let the other closed circuit, which 
includes the second wire, be moved closer to it, and the current 
induced will resist the motion. It will be a current in the oppo- 
site direction. If separated the induction will resist the separa- 
tion, and the currents will be similar in direction. 

Lenz's law is best taken with its due limitations — that it only 
applies to the relations of electro-magnetic induction to mechani- 
cal motion causing it or produced by it. It is not a good practice 
to try to stretch it to cover induction where there is no mechani- 
cal motion. 

Foucault or Eddy Currents.— If a conductor should be so 
moved in a field of force that the number of lines of force pass- 
ing through it at an angle with its direction of motion vary, a 
current will be produced within it. This current will circle 
around in its mass, will absorb energy and expend it in heating 
the metal. Such currents are called Foucault or eddy currents. 
A set of infinitely thin conductors with ends unconnected moved 
through a field, if insulated from each other, would require the 



216 



ELECTRICIANS' HANDY BOOK. 



expenditure of no energy, on the assumption that being of infinite 
thinness, no electric circuit can exist in them. If their ends were 
connected by a conductor under the conditions already specified 
as to variation in density of field, then a current would fiow and 
energy would be absorbed. If a heavy solid conductor were sub- 
stituted for the infinitely thin ones, while local currents would 
be established in it, there would be no through current all in 
one direction caused to pervade it. If its ends were connected 
by a conductor such a through current would be established. The 
local currents in the mass of the conductor are Foucault or eddy 
currents. 

Variations in Impressed Electromotive Force, — ^^The conduc- 
tor which cuts the lines of force forms part of a circuit, and in 




Fig. 123.— Closed Loop in a Bipolar Field. 
cutting the lines of force either increases or diminishes the lines 
of force threading or interlinked wifli the circuit. The conductor 
indicated in the diagram. Fig. 118, starting at the left of the 
pole, cuts lines at a comparatively slow rate. This is because the 
lines are not so densely placed as directly opposite the pole. 
Hence a relatively small electromotive force is impressed upon 
it at the distant point. It cuts more and more lines of force in a 
second as it approaches the pole, thereby changing the number 
of interlinked lines with greater and greater rapidity, so that the 
electromotive force, and consequently the current, is strongest 
when the conductor is opposite the pole. It then, for like rea- 
sons, diminishes as the conductor recedes to one side of the pole 
in its motion. Such a conductor is shown in Fig. 122, reproduced 



INDUCTION. 217 

from a preceding page. There is another case the opposite of this. 
The conductor described is a part of a circuit the plane of whose 
moving portion is in line with the axis of the magnet when the 
armature conductor is opposite the center of the pole. Suppose 
the current is to be induced in a flat coil swept across the pole, 
and that the coil is perpendicular to the magnet axis when the 
coil faces the pole. Such coils are shown in Fig, 120, 

Such a coil will be interlinked with the greatest number of 
lines of force when opposite the pole, but its change rate will at 
that point be the lowest. The current induced by the impressed 
electromotive force will be least at this point. 

This condition obtains in many alternating-current generators. 
The maximum electromotive force is induced when the armature 
coils are midway between two poles; the electromotive force is 
zero when the coils are opposite the poles and in the densest 
field. 

Direction of Current Induced ia Coils. — The direction of the 
current induced in a coil is determined by Lenz's law. If it ap- 
proaches a north pole the currents induced will oppose its ap- 
proach; they will therefore be the reverse of the Amperean cur- 
rents or of the currents in the magnetic coils. As the coil recedes 
the currents will reverse also by Lenz's law so as to oppose the 
motion, and will coincide in direction with those of the magnet 
poles. 

Fig. 120 and several other cuts illustrate the principle. The 
poles of a magnetic field are shown facing the observer; the direc- 
tion of the induced currents is shown by the curved arrows. The 
coil in which current is being induced is moving in the direction 
indicated by the arrow. Arrowheads are marked on the coils to 
show the direction of the currents induced. When directly oppo- 
site the pole there will be no change in the number of lines of 
force passing through the coils, and no currents will be induced 
in them. 



CHAPTER XL 

DIRECT-CURRENT GENERATORS ANJDi MOTORS. 

Dynamo = Electric Generators.— Electric energy is now almost 
universally produced on the large scale by dynamo-generators 
including the following parts: 

A strong magnetic field or fields are produced by one or more 
electro-magnets. The magnetic circuits include the core of the 
electro-magnets and a mass of iron between or near their poles 
which constitutes the armature core. Coils of insulated copper 
wire are wound upon the armature cores. By mechanically 
changing the relations of armature windings and fields of force 
electromotive force is impressed upon the circuit and a current 
results. The product of electromotive for'^e and current is elec- 
tric power. Mechanical energy is required to operate the mechan- 
ism for changing field and armature coil relations. This energy 
is absorbed by the machine, and electric energy is produced in 
its stead. 

The easiest way to understand the dynamo, as it is often 
termed, is to follow up the construction from the simpler to the 
more complicated types. 

Interchangeability of Dynamo and Motor. — The interchange- 
ability of dynamo and motor stands as the subject of one of the 
greatest discoveries in electric engineering. Electric motors had 
been constructed for many years before it was definitely decided 
that the same machine could receive electric energy and convert 
it into mechanical energy, thereby constituting itself a motor, 
or could be operated by a steam engine, water turbine, or other 
prime motor, receive mechanical energy, and convert it into elec- 
tric energy. It then is a generator or dynamo. 

As dynamos are calculated to give a definite electromotive 
force and current, and as motors are calculated to absorb a definite 



Direct-current generators and motors. 219 

electromotive force and current, the calculations for motor and 
dynamo are on the same lines. 

Varieties of Dynamos. — There are two grand divisions of dy- 
namos; one is for the production of the direct current, which is a 
current of unchanging direction; the other is for the production 
of the alternating current, which is a current reversing its direc- 
tion periodically, in practice from twenty times upward a second. 

Although a current which changes in direction may be consid- 
ered as an aggregation of different currents of opposite direction, 
this aggregation is always called an alternating current, and is 
treated as a variety of single current. 

The principal constituent parts of a dynamo are the field, con- 
sisting of core and winding; the armature, consisting also of core 
and windings; the collecting rings or commutator and brushes. 
The field and armature vary in construction, their windings vary 
in system, and from these variations many varieties of dynamos 
are derived. 

Elementary Idea of an Alternating-Current Dynamo..— As- 
sume a bipolar (two-pole) field which in the cut. Fig. 122, is indi- 
cated by two magnet poles facing each other and marked N and 
S. Let a simple rectangle of wire such as shown be rotated 
about an axis, a &, in such a field. As one side sweeps across 
the north pole the other sweeps across the south pole, and electro- 
motive fouce of opposite polarity is impressed on the two sides of 
the rectangle, so that a current is produced through it. This 
current is strongest when the cutting conductors are passing the 
poles, sinks to zero or nothing when the plane of the rectangle 
is at right angles to the lines of force extending from pole to 
pole, and reverses in direction as this point is passed. During 
half the revolution the current flows in one direction, and dur- 
ing the other half in the other. This constitutes a dynamo. 

Collecting or Slip Rings. — In this dynamo the current is con- 
fined to the rectangle, which is supposed to be a continuous con- 
ductor insulated from the axle. Suppose it to be cut at one end 
at the axle, and let the ends be connected each to its own ring 
fastened around the axle and insulated from it. The rings are 
also to be insulated from each other. If the recta.ngle is rotated, 
electromotive force of alternating polarity will be impressed 



220 



ELECTRICIANS' HANDY BOOK. 



upon it, but as it is an open circuit, no current will be produced. 
Let a spring bear against each ring, and let a wire of greater 
or less length connect the springs. The circuit is thus closed, 
and currents first in one direction and then in the other flow 
through the whirling conductors and the wire. The rings are 




Fra. 133.— Use of CoiiiiECTiNG or Slip Rings. 



called collecting rings. The currents are treated as one and 
are called an alternating current. The arrangement is shown in 
Fig. 123. 

Brushes. — The springs which bear upon the collecting rings or 
commutators are called brushes. Often instead of springs, blocks 

of carbon, pressed by 
^ springs, are used. The 
brushes must be insul- 
ated from the frame of 
the machine. 
^ /^^^^^^^^^^^^^^^ Elementary Idea of 

-^^^^^^^sss^cs^jss^ 2^^U^^ - .,^^:§^^$^:^:$$$$j:^^^ ^ Direct= Current Dy= 

^^^^^^^ I"r=!Tr____^^^^^^^ namo. — In the next 

Fig. m.-BECTANGLE COKNECTED TO ^^^' ^^^- ^^^' ^^^ ^^^' 

Commutator. tangle is shown with 

its ends connected to 
segments of rings, each one as nearly as possible 180° or a 
half circumference in extent. They are insulated from each 
other and insulated from the shaft and attached to it. Springs 
at opposite sides press against them. The segments constitute 
a commutator, whose section is shown in Fig. 125. Let the rec- 
tangle in Fig. 124 with its two-part commutator be rotated in the 




DIRECT-CURRENT GENERATORS AND MOTORS. 



521 



two-pole field. Let the springs which are insulated from each 
other be connected by a wire. As the rectangle passes the points 
where no current is generated, the springs pass from one com- 
mutator division to the other. As current goes in one direc- 
tion through the rectangle, it is delivered to springs in one 
sense. As the current reverses in the rectangle, it is delivered to 
the springs in the other sens^, because as the current changes, 
the springs change their contacts with the commutator segments. 
Hence the wire connecting the springs receives currents varying 
from zero intensity up to a maximum, but always in the same 
direction. 

Increasing the Electromotive Force by Increasing the Turns. 
— ^The electromotive force is proportional to the lines of force 
cut per second by the whirling conductors. It may be increased 





Fig. 135.— End 
View of Two- 
PiECE Commu- 
tator. 



Fig. 126.— Double Eectangle 
Connected to Two- Part 

COMMUTATOB. 



by increasing the turns in the rectangle. In Fig. 126 they are 
shown doubled (the dotted line is the axis of rotation) and they 
may be increased any number of times. The turns are insulated 
from each other and are continuous. Doubling the turns doubles 
the electromotive force, and so on. 

Increasing the Electromotive Force by Adding an Armature 
Core. — The field may be made denser by filling the space between 
the poles as completely as possible with a mass of iron. This is 
done by providing a cylindrical Iron core, which almost fills the 
gap between them, and winding the wires on that. The denser 
field giving more lines of force, it follows that more lines of 
force are cut per second, and that a higher voltage results. 

Armature and Core. — The iron cylinder with the wire wind- 
ings constitutes an armature. The iron cylinder alone is the 



222 



ELECTRICIANS' HANDY BOOK. 



armature core. The wires are the windings of the armature. 
Bach convolution of the wire is called a turn. 

Field Poles. — The early magnetos, dynamos, and motors were 
based on the horseshoe or U-shaped magnet as a producer of the 
field of force. Where a single magnet was used, this constituted 
a two-pole or bipolar construction. 

Recent practice favors the use of more than two field poles, or of 
multi-polar dynamos. In these as a rule each pair of poles in- 
duces two parallel currents, and in typical winding there is a 
brush for each pole, and the brushes are spaced at equal angles 
around the commutator. 
As a general rule, the number of poles is even; there are as 

many north poles as there are south 
poles. The poles alternate with each 
other, a north pole coming next to 
a south pole. Fig. 127 shows a sec- 
tion of a four-pole field with arma- 
ture core, the lines of force being in- 
dicated by arrows. 

Dynamos and motors can there- 
fore be classified from their number 
of field poles as bipolar, four-pole, 
six-pole dynamos. Two general di- 
visions are bipolar dynamos and 
multipolar dynamos, the latter in- 
cluding all except bipolar ones. 
Open=Coil Armatures. — The ele- 
mentary armatures described up to this are open-coil armatures. 
They may have any number of coils and any number of 
turns in each coil. Open-coil armatures are used in practice 
principally on the Brush and Thomson-Houston dynamos. In them 
they are greatly developed from anything shown here. They are 
used in great number on testing and signaling magnetos. The 
name open coil is given to them because no closed circuit can 
exist in their windings; the outer circuit has to be connected to 
the brushes to give a closed circuit. 

Spindle or H Armature. — The spindle or H armature had in 
early days a considerable vogue. It is now definitely abandoned 




Fig. 137.— Multipola-r Field 
AND Armaturk Core with 
Magnetic Circuits Indicated 



DIRECT-CURRENT GENERATORS AND MOTORS. 223 

in favor of better constructions, except for very minor uses. It 
Is a single-division drum armature. The contour of the core is 
that of a cylinder with two grooves running lengthwise of its 
su-rface and diametrically opposite to each other. The cross sec- 
tion of such an armature represents a sort of letter H, whence 
one of its names was derived. It was a very distinctive armature 
with Werner Siemens in his early machines. It had a two-bar 
commutator and was an open coil. 

It was a poor form, as it had low permeance and inevitably 
gave a highly pulsatory current, as it only admitted of two di- 
visions in the commutator. The cut. Fig. 128, shows this arma- 
ture. 

Closed-Coil Direct=Carreiit Armature^ — This is a type whose 
windings are so connected as to form a closed circuit. This is 
irrespective of the brushes. The great majority of machines have 
this type of armature. 




Fig. 128.— Siemens's Spindle or H Armature. 

The characteristic current distribution in a closed-coil direct- 
current armature involves parallel currents in its windings. 
In a two-pole dynamo the current in one half of the windings 
is parallel to that in the other. In a four-pole dynamo there are 
four divisions, each with its own current in parallel with that 
in the next division. The same principle applies to any num- 
ber of poles. The collecting brushes are in typical constructions 
equal in number to the poles. 

While the above is true for most dynamos, the windings of 
the armature can be greatly modified, so as to bring about differ- 
ent current distributions. The above are characteristic, and 
represent the usual practice. 

It follows that the currents in a closed-coil direct-current arma- 
ture never go through the winding consecutively. The brushes 



224 ELECTRICIANS' HANDY BOOK. 

are placed on the commutator at points where parallel currents 
meet. When the outer circuit is open, the electro-motive forces 
induced meet at these points and neutralize each other, so that 
no current is induced in the windings, although they are in closed 
circuit. 

Cutting Lines of Force Without Change in Number of Inter= 
linking Lines can also produce a current. The circular con- 
ductors which have just been illustrated as having no current 
produced in them, although they cut lines of force, have electro- 
motive force impressed upon them. But the electromotive force 
can be located in halves of the ring separated by a diameter, in 
a general way perpendicular to their direction of motion. The 
electromotive force in one half is of similar polarity to that in 
the other half, so that they oppose each other and no current is 
produced. Electromotive force cannot exist without the possibility 
of a current being produced by it. A current by some mechanical 
arrangement could be taken from the extremities of the diameter 
of the ring without any change in number of interlinking lines of 
force. A machine in which this is done is called a homopolar, uni- 
polar, or acyclic generator, and is described very briefly else- 
where. It has not gone into very extensive use, although it 
probably has a future. 

The ordinary generator produces its effects by so cutting lines 
of force that the number interlinking the circuit changes as they 
are cut by the conductor. Without such change no current would 
be produced in ordinary machines. The point is mentioned here 
to fix the fact that the cutting of lines of force is what pro- 
duces electromotive force, and that the variation in number of 
interlinking lines is something which happens in ordinary gen- 
erators when the lines of force are cut. In homopolar dynamos 
the above variation does not occur. The cause of impressment 
of electromotive force is the cutting of lines of force, not the 
variation in interlinking lines of force. 



CHAPTER XII. 

DIRECT-CURRENT ARMATURE WINDING. ' 

Armatures. — The function of an armature is to support con- 
ductors forming part of an electric circuit, which are to be sub- 
jected to the action of a field of force whose relation to the wind- 
ings constantly varies. With fixed relations of the field to the 
armature conductors there would be no current induced in ma- 
chines of the usual type as here described. 

The relations are varied, so as to induce current by the sweep- 
ing of conductors and field poles past each other. This is univer- 
sally done by having the poles and armature coils arranged on a 
circle; and by rotation of either armature or field, or by rotation 
of a series of "inductors" of soft iron past the poles, the desired 
varying of relations is brought about. 

Armatures are wound in many ways. For direct-current work 
the closed-coil drum armature is much used. It is the successor 
of two historical inventions, the Pacinotti disk armature and the 
Gramme ring armature. In both of these the closed-coil feature 
appeared, which characterizes most modern dynamo and motor 
armatures. 

The Pacinotti Armature, — ^The modern armature is with a 
few exceptions wound on principles exemplified by the famous 
Pacinotti (pronounced Pacheenot-tee) armature of 1864. These 
principles require the winding to be consecutive from beginning 
to end, so that the windings form one closed circuit. Such a 
winding is characterized as re-entrant when in the winding the last 
end falls into place, so as to be in line with the first end. 

The winding is carried out as symmetrically as possible, and 
at symmetrical points it is connected to divisions of the com- 
mutator. 

Pacinotti described his armature in 1864; it constituted part of 



226 ELECTRICIANS' HANDY BOOK 

a motor. It was a disk-shaped armature mounted horizontally 
and wound with a continuous winding of wire and with sixteen 
connections from the windings to sixteen insulated bars on the axis 
of the disk, which bars constituted a commutator. Under the disk 
was a circle of iron polarized by an electro-magnet underneath it, 
and whose legs rose vertically to opposite extremities of a diam- 
eter of the iron ring. This produced two opposite poles on the 
ring. 

There was here embodied the salient features of the modern 
dynamo, its continuous winding and commutator with numer- 
ous divisions, each connected to the winding. A toothed iron 
ring with wooden pegs or projecting pieces of boxwood formed 
the core on which the armature windings were made. 

Pacinotti had no idea that by turning the armature mechanic- 
ally a satisfactory current could be produced. His motor con- 
tained the elements of a dynamo unknown to himself. 

The Gramme Ring, named from the inventor Gramme, was de- 
scribed in the Comptes Rendus (Paris) in 1871 and 1872. It was 
patented in 1870. It is a type of armature which acquired an 
immense vogue, and became in a sense one of the scientific glories 
of France. It is not much used in this country, where the drum 
armature is generally adopted. The Brush and Thomson-Houston 
open-coil dynamos are the principal American machines using it. 
But abroad many ring-armature machines are built. 

Gramme's original ring core was made smooth and of circular 
cross section and was entirely overwound with wire. 

riodern Types of Closed=CoiI Armatures. — The modern arma- 
tures may be grouped into four classes: Ring armatures, drum 
armatures, pole armatures, and disk armatures. The»ring arma- 
tures are based on the Gramme ring. The drum armature is 
sometimes taken as being derived from a Gramme ring by filling 
up the central opening with iron. The pole armature recalls an 
early type, and finds one of its great applications in alternating- 
current machines. The disk armature dates back to one of 
Pacinotti's machines. 

In modern American practice the ring and disk armatures are 
not much used. 

Armatures for direct current vary from those designed for al- 



DIRECT-CURRENT ARMATURE WINDING. 



227 




Fig. 129. 



-Two-Paet Gramme Ring 
Armature. 



ternating current. The latter will be described by themselves. 
The ring armature may be taken as to a certain extent the pro- 
totype of the drum armature, and will be first treated. 

The two-pole or bipolar dynamo is a little simpler than the 
multipolar one, and will 
be the starting point for 
the description of arma- 
ture windings. 

The Gramme ring is a 
ring of soft iron on which 
the armature coils are 
wound. Fig. 129 shows in 
diagram a ring, supposed 
to rotate about an axis 
perpendicular to the pa- 
per in the two-pole field. 

The dotted lines show the course of the lines of force. The ac- 
tive parts of the armature windings are those on the outside of 
the ring. It may be made more complicated and efficient by 
doubling the parts, as in Fig. 130. B^ and Bo are the conductors 
from the brushes; at A and C no current is induced; at D and E 

the maximum is induced. 
The arrows give the 
course of the currents, 
and show how they meet 
in opposite commutator 
sections. The windings 
operate in parallel of two 
To make a real working 
armature, a large number 
of windings are requisite, 
and the commutator is 
divided into many sub- 
divisions. Such a ring 




Fig. 130.— Four-Part Gbammu Ring 
Armature Showing Course op Current. 



is indicated in diagram in Fig. 131. 

Commutator Connections of Ring Armature. — In practice a 
commutator is mounted on the shaft, and wires are led from 
the windings of the ring to it, and the brushes bear against the 



22S 



ELECTRICIANS' HANDY BOOK. 



commutator and take current from it. The wires are led from 
symmetrically or evenly spaced portions of the winding, and 




Fig. 131.— Gramme Ring Armature Showing 
Commutator Connections. 



each one is connected to its own commutator segment or leaf. 
The commutator is used from mechanical considerations, other- 
wise the current could be taken from the conductors on the out- 
side of the ring, as indicated in the diagram. Fig. 132. 

Cores of Ring Armatures 
were originally made of iron 
wire wound into a circle of any 
desired thickness. Present prac- 
tice makes them of thin ring- 
shaped laminations. A closed 
ring is somewhat troublesome 
to wind, so ring cores are often 
made in two semi-circular 
halves, over which the coils al- 
ready made up can be thrust, 
after which the two halves are 
bolted together, so as to form a 
ring. 

Permeance of the Ring Core. 

— One of the objections to the 

ring core for two-pole machines 

is its low permeance as compared with a drum core. Every effort 

may be made to reduce the central opening of the ring, yet it is 




Fig. 133.— Relation of Gramme 
Ring to Commutator Brushes. 



UlKliJVT-iJUHKENT ARMATURE WINDING. 229 

not easy to imagine a ring armature core of as high permeance 
for a bipolar field as a drum armature core would be. 

The cross section of the core varies greatly with different con- 
structors. The modern appreciation of the laws of the magnetic 
circuit has led to the production of ring cores of good per- 
meance. Some of the older rings were thin, and consequently of 
low permeance. For multipolar machines a ring armature may 
have about as good permeance as that of a drum armature. This 
is on account of the course taken by the lines of force, which go 
into the core and out of it within a small portion of its circum- 
ference. In a multipolar machine they follow a U-shaped path 
from pole to pole, largely through the outer layers of the core. 
In the bipolar machine the lines of force have to go from one 
side of the ring to the other. This develops the bad permeance 
of the ring armature to the highest degree, as the lines of force 
following the curved path of the core have a longer distance to 
travel than that followed by them in going directly across a drum- 
armature core. 

In plain ring winding there is a brush for each pole, which 
brushes normally collect current from points of the commutator 
nearly symmetrically located between the poles, so that a like 
difference of potential exists between each pair of contiguous 
brushes. By special winding one pair of brushes can be made to 
answer for a multipolar machine. This has the objection that 
it leads to unsymmetrical positions of the brushes, with conse- 
quent uneven voltage between the brushes appertaining to the 
two sides of the commutator. 

Idle Wire. — In the ring armature the wire on the outside of 
the ring is the active portion. All on the inside is idle as far as 
the impressment of electro-motive force is concerned. This is one 
of the objections to this type, an objection which is of some mo- 
ment, as low resistance in the armature is an element of effi- 
ciency. 

Current in a Ring Armature. — The course of the currents in 
a ring armature in a bipolar field is shown in Fig. 133, in which 
the arrowheads show the direction. The currents meet at two 
points at the extremities of a diameter which is at right angles to 
the diameter determined by the axes of the poles. This axis is 



230 



ELECTRICIANS' HANDY BOOK. 



marked A B. The arrowheads indicate the current in the eight 
coils. The impressment of electromotive force which causes 
the current is principally in the coils 2, 3, 6 and 7 of the arma- 
ture in its present position, but the armature is supposed to be 
turning, so that the coils acted on are constantly different ones. 
The brushes remain fixed in position, indicated by the line A B. 
The arrows under N and S are supposed to be one in front of and 
the other behind the core, and indicate the current which will 
be impressed by the induction of the poles. The curved arrow 
denotes the direction of rotation of the core. 

Open - Wound Fcur = Part 
Ring Armature. — In Fig. 134 
B1B2 indicate the brushes 
which are taking current 
from the horizontally-placed 
pair of coils. These are in 
the position in which the 
highest degree of electromo- 
tive force is impressed upon 
them; and during the period 
of such active impressment, 
the brushes receive current 
from them. After a rotation 
of about half the arc of the 
commutator division, the coil 
is open-circuited, and the 
other one has its circuit 
closed, as the brushes come in contact with the commutator sec- 
tions connected to it. This illustrates the principle of the open- 
coil armature. It apparently fails to utilize half the ring sur- 
face, but in any case one-half of this surface represents the locus 
of impressment of by far the greater part of the electromotive 
force. The arrows have the usual significance. 

Mounting of a Ring Armature. — The diagram showing the 
relations of a ring armature to its field in a series-wound dyna- 
mo is shown in Fig. 135. The field magnet i-^* wound to give 
consequent poles, N N and S S, above and below the vertical diam- 
eter of the ring R. The current is taken from the opposite sides 




Pig. 133.— Currents in the Gramme 
Ring Armature. 



SE^sss^M^nr' 



DIRECT-CURRENT ARMATURE WINDING. 



231 




Fig. 134.— Open-Coil Ring Abmaturb. 



of the commutator and goes through the field coils. The axle 
A B of the armature is journaled in the magnet yokes. 

Multipolar Ring Armature.' — The ring armature can be used 
in a multipolar field with- 
out change. All that is 
necessary is to have, more 
brushes than two, so as 
to take the current off 
from several parts of the 
winding. If the currents 
in a Gramme ring are 
traced, it will be found 
that neutral points are es- 
tablished equal in number 
to 4;he poles of the field. 
If the winding and com- 
mutator connections are symmetrical, the neutral points will lie 
midway between the radii which go through the axes of the 
poles. The current is easily traced by following the rule given 
on page 210, and treating the parts of the wire outside the ring 
as conductors corresponding to the arrows of the diagram on the 

same page. It is in any 
case obvious that if the 
current is induced in 
one direction in front of 
the north pole, it will be 
induced in the other di- 
rection in front of the 
south pole. The cur- 
rents therefore meet 
midway between the 
poles, and are to be 
taken thence by a brush. 
This brings a brush 
midway between each 
pair of poles, so that they aggregate one brush for each pole. The 
development of a four-pole ring winding is shown in Fig, 136. 
The Drum Armature,— It has been noted that the wire on 




Fig. 135.— Diagram ov "WiNDTNa ov a 
Gbamme King Series Machine. 



232 



ELECTRICIANS' HANDY BOOK. 



tlie outside of a ring armature is the active part. The large 
opening of the ring decreases its permeance. If the opening 
were filled with iron and the idle wire suppressed, one improve- 
ment would result — the lowering of reluctance or increasing of 
permeance, and in some cases there would also be brought about 
a reduction of resistance. If a reduction of resistance occurs, it 
is due to the reduction in length of the wire. This reduction 
is to be looked for in the transition from a thick ring core with 
small central aperture to the drum core — not in the transition 




Fig. 136.— Development of a Four-Pole Ring Armature. 



from the old-style thin-bodied ring core with large central aper- 
ture. 

In the ring armature shown in Pig. 131 imagine the center open- 
ing filled with iron and the inner wires removed. Other leads 
must be carried across the two ends, so as to bring the whole 
quantity of wire into one consecutive coil, and from symmetrical- 
ly-located points on the windings leads must be carried to a com- 
mutator. This gives a drum armature. 

A drum armature is unlike a ring armature in one respect. If 
wound for a bipolar field, it will not operate properly in a four- 
pole or other multipolar machine. In a six-pole field it would 
give some result; in a four-pole field, none. 



DIRECT-CURRENT ARMATURE WINDING. 233 

Action of the Drum Armature, — ^A conductor on the periphery 
of a drum armature swept across a field pole has impressed upon it 
electro-motive force the reverse of that impressed upon one swept 
past the opposite pole. If the current induced flows to the com- 
mutator end in one conductor, it will flow away from it in the 
opposite conductor. It follows that to obtain a continuous cur- 
rent such conductors should be connected to each other. Then 
the current as the circuit is completed will flow in one direction 
through one active wire, then across the end of the core in tho 
connecting wire, in the reverse direction in the other active wire, 
and across the other end. If the wires correspond in angular 
distance to two opposite poles, this course of current will be 
given by the impressed electromotive force. This is the reason 
why wires opposite a north pole must be connected to wires op- 
posite a south pole. 

If a wire were connected to one directly opposite on both ends, 
there would simply be a series of short-circuited conductors, ag- 
gregating as many complete short circuits as there are leaves 
or bars in the commutator. 

To secure a continuous winding, the conductors exactly op- 
posite are not directly connected. Direct connection is made as 
described between conductors nearly but not quite opposite to 
each other. With every cross or end connection a step in ad- 
vance (wave winding) or a step in retardation followed by a 
longer one in advance (lap winding) is made. The final result 
is the same in either case; a uniform progress around the cylin- 
der is made by the windings, somewhat similar to a spiral. 

Drum Armature Windings. — To form an idea as easily as pos- 
sible cf the essential features of the drum winding, an example 
may be given of a winding with very few conductors. 

The winding of a drum armature may be divided into three 
classes or parts. The first are straight lines of wire or con- 
ductors which cut the lines of force. These lie upon the cylin- 
drical surface of the core, parallel with its axis. 

If we stop here, we have simply a lot of short straight pieces 
of insulated wire occupying the places of the elements of a cylin- 
der. They are of the same length as the core. The commutator 
end of the armature may be termed its front end. The straight 



234 ELECTRICIANS' HANDY BOOK. 

conductors now must have their ends connected across the front 
and rear ends of the core. The rule which must be followed 
for closed-coil winding is that each wire must be connected to 
one at an angular distance from i'. corresponding approximately 
to the interval between the nearect north and south poles. For 
two-pole fields such as are now being described this distance is 
approximately 180°. At the back of the armature, wires run 
across its surface connecting the conductors on the periphery of 
the drum or cylindrical core, subject to the rule just stated. 
These operate with the front connections to connect all the wind- 
ing into one continuous circuit. At the front each of the wires 
lying on the cylindrical surface is connected to an armature bar. 
To the same bar is connected a wire connected to an opposite 
conductor, which is approximately 180° distant from the first 
one in a two-pole field. If it were a four-pole field, the angular 
distance would be approximately 90°. 

SimpleSystemof Armature Winding.— In a simple type of bi- 
polar winding the rear end of a wire might connect with one 
which would be one wire out of perfect opposition. In front it 
would connect to a commutator bar. The same commutator bar 
would then connect to another wire nearly opposite, which would 
be near to the one with the rear connection. This if repeated 
would join all the wires into one continuous lead. The number 
of commutator bars would be equal to one-half of the peripheral 
surface wires. 

Eight= Conductor Drum Armature. — Suppose there were eight 
surface conductors or wires. Starting with any desired wire, let 
them be numbered consecutively. As the most natural way, we 
may start with wire 1. In front it is connected to a commutator 
bar, which we may designate as a. From this commutator bar 
the second connection runs to wire 4. This is one less than half 
tha wires. The rear end of wire 4 is connected across the rear 
of the core to wire 7. Now returning to the front or commuta- 
tor end, wire 7 is connected to commutator bar cZ, and the second 
connection from commutator bar d goes to the front end of 
wire 2. Counting forward, this is one less than half the number 
of wires. The rear end of wire 2 connects with the rear end of 
wire 5. The front end of wire 5 connects through the commu- 



DIRECT-CURRENT ARMATURE WINDING. 



235 



tator bar c to wire 8, also an interval of one less than half the 
wires. The rear end of wire 8 connects to the rear end of wire 3, 
and the front end of v/ire 3 through the commutator bar & con- 
nects with wire 6. The rear end of wire 6 connects with the rear 
end of wire 1. This closes the circuit. 

A winding table for the above is given here. 

1 a 4 indicates that wire 1 connects through a to wire 4. 

7 d 2 that wire 4 connects to wire 7, that wire 7 connects 

5 c 8 through cl to wire 2, and so on as explained. 

3 & 6 above. The letters a, b, c, and d denote bars of the com- 
mutator. 

Twelve= Conductor Bipolar Armature. — ^The winding of this is 
shown in the diagram, 
Fig. 137. The dotted 
lines indicate the wires 
crossing the distant end 
of the core, the full lines 
those crossing its front. 
Again a departure of one 
wire from 180° angular 
distance is adopted. "Wire 
1 connects in front with 
wire 8 and on the rear 
with wire 6. Wire 1 to 
wire 7 would be 180° 
angular distance, whence 
it is evident that the 

winding is based on a departure from 180° of an interval of one 
wire. The commutator sections should be six in number, and 
should connect to the centers of the set of conductors which cross 
its end of the core. 

Sixteen=Conductor Bipolar Armature. — The winding is shown 
on the basis of a departure of one wire from 180° in Fig. 138. 
The neutral line is shown at right angles to the polar axis of 
the field. On part of the circles representing the end view of the 
active conductors crosses are marked. These indicate that the 
current in those wires goes away from the observer. The circles 
with central points indicate that in the conductors they repre- 




Fig. 137.— Twelve-Conductor Bipolar 
Drum Armaturb Winding. 



236 



ELECTRICIANS' HANDY BOOK. 



sent, the current is coming toward the observer. To remember 
this system, the points may be taken as indicating the points 
of arrows flying toward the observer and the crosses as indicat- 
ing the feathers of arrows flying away from the observer. This 
system of indication is often used in textbooks. 




Tig. 138.— Sixtben-Condenser Bipolar Drum 
Armature Winding. 

Winding Tables.— The winding tables for these three armatures, 
omitting commutator bar letters, are as follows: 

Eight-Conductor. Twelve-Conductor. Sixteen-Conductor. 



1 a 4 


1 


8 


1 


8 


7 d 2 


3 


10 


15 


6 


5 c 8 


5 


12 


13 


4 


3 & 6 


7 


2 


11 


2 




9 


4 


9 


16 




11 


6 


7 
5 
3 


14 
12 
10 



In the twelve-conductor winding, wire 6 connects with wire 1, 
and in the sixteen-conductor winding wire 10 connects with wire 



DIRECT-CURRENT ARMATURE WINDING. 



237 



1, thus making the windings re-entrant. The windings may be 
studied out on the cuts, when the full significance of the wind- 
ing tables will be apparent. 

Windings for Multipolar Fields,— In bipolar winding, every- 
thing in the way of the spacing of conductors is referred to 180°, 
or to one half of a circumference. The cross connections over 
the ends of the drum core connect conductors separated a little 
more or a little less than 180° from each other. The angular 
distance 180° is the distance 
from center of pole face to 
center of pole face. 

When a drum armature is 
wound for a multipolar field, 
the angular distance between 
adjoining north and south 
poles is substituted for the 
180° of bipolar winding. 

Suppose that there are 
eighteen conductors on the 
cylindrical surface of the 
core. This gives four and a 
half conductors to each pole 
if there are four poles in the 
field. The quarter circumfer- 
ence is the controlling factor. 
Conductor 1 in bipolar wind- 
ing might connect to number 12 or 14; in four-pole winding it 
may connect to number 6, number 6 to number 11, and so on, 
going five conductors at each connection. 

Eighteen = Conductor Four=Pole Armature. — This four-pole 
winding with eighteen conductors is illustrated in Fig. 139 in 
diagram as hitherto, and in Fig. 140 a circular development of 
the identical winding is given. The dark spots near the center 
of the latter diagram indicate the points where the brushes take 
the current. The outer lines forming the points of the star are 
the connections crossing the rear end of the core, and corre- 
spond to the dotted lines of Fig. 139. The short straight lines 
running from inner circle to outer circle represent the straight 




Fig. 139.— Eighteen -Conductor 

FouK-FoLE Drum Armature, 

Wave Winding. 



238 ELECTRICIANS' HANDY BOOK. 

conductors on the periphery of the drum. The cylindrical surface 




Fig. 140.— Circular DKVEiiOPMEST of Armature Winding. 



of the drum is represented by the annular area between the two 

circles. The lines within the 
inner circle represent the con- 
nections at the front or commu- 
tator end of the core. 

Circular Developments are 
used a great deal to illustrate 
armature windings. The points 
outside the rings have no real 
existence as shown. They mere- 
ly indicate the center of the cross 
connections over the head of the 
armature core. 

Commutator Connections are 
shown in Fig. 141, a fourteen- 
section armature winding with 
seven commutator divisions. 
Wave and Lap Winding.— There are two divisions or classes of 




Fig. 141.— Commutator Connec 

TioNS in Fourteen-Conductob 

Drum Armature. 



DIRECT-CURRENT ARMATURE WINDING. 



239 



winding for drum armatures, named as above. In the first a 
uniform progression is obtained in the winding; in the second 
a retrograde step of a definite number of conductors is followed 
by a forward step of a larger number. Thus in wave winding 
each step is progressive; in lap wave winding the sum of every 
two steps is progressive. The development of these windings most 
obviously shows the origin of their names. An example of the 
development of wave and lap winding for an armature with 
eighteen peripheral conductors will be shown. 
Wave Winding. — The peripheral or active conductors are rep- 




FiG. 142.— Development of Eighteen-Condttctor Wave Winding. 



resented in Fig. 142 as vertical lines and numbered from 1 to 
18. The cross connections at one end of the drum core are rep- 
resented by the lines of V-shaped connections above the vertical 
lines; the cross connections at the other end of the core are 
represented by the V lines below the vertical lines. If the 
reader will follow the course of the wires with a pointer of any 
kind, he will see that there is a wave-like progress. The winding 
is exactly what is shown in Figs. 139 and 140. 

Lap Winding. — The next cut, Fig. 143, shows the same arma- 
ture with eighteen conductors as before, but with lap winding. 
Thus on the top of the diagram a wire starts from conductor 1 
and goes to the right to conductor 6, which is five conductors 



240 



ELECTRICIANS' HANDY BOOK. 



in progress. From conductor 6, instead of going forward tlie 
winding goes back on itself, or to the left to conductor 3; from 
conductor 3 the lead goes forward to conductor 8; then back to 
conductor 5, and so on. This ends by the winding from conduc- 
tor 17 going forward to conductor 2 and back to conductor 1. 
This ends the winding and leaves it re-entrant. Thus the wind- 
ings form a series of laps, going forward five sections and back- 
ward three sections, gaining two divisions for each two steps. 
Development of Commutator Connections. — The commutator 
bars are shown in the development as little rectangles, and they 




Fig. 143.— Development of Eighteen-Conductor Lap Winding. 



are indicated by small letters. There is one bar for each pair of 
nearly opposite conductors, and in the development they are 
shown connected to the angles, either above or below the dia- 
gram. These angles in the development simply represent the 
centers of the end windings, which go across the ends of the 
drum; they do not necessarily represent any angle or bend in 
the wire. 

Development of Field Poles. — These are represented back of 
the diagram, and each one is marked N or S according to its 
kind, whether north or south pole. 

Development of Current Induced. — This is determined for 



DIRECT-CURRENT ARMATURE WINDING. 



241 



drum windings by tlie rule given on page 210, and the field poles 
in the diagram are shaded diagonally in accordance with that 
rule. If the conductors are carried from left to right, those in 
the range oS. the north pole will have downward currents in- 
duced in them, when the outer circuit is closed; those in the 
range of the south pole will have upward currents induced. 
Arrowheads are drawn to follow out this induction, and where 
the currents meet on the commutator, the brushes take off cur- 
rent to the outer circuit. 

A twenty-four conductor 
four-pole lap winding is 
shown in Fig. 144. 

Straight Developments. 
—The cuts. Figs. 136, 142 
and 143, show a system of 
development much used in 
illustrating armature wind- 
ings. It is defective be- 
cause it has disconnected 
ends. If the paper were 
bent into a cylinder, these 
disconnected ends would 
come together, and the 
winding would form a 
closed circuit or be re- 
entrant. As drawn, this 
connection has to be as- 
sumed, just as the circular 
contour has to be assumed. 

Winding a Drum Armature. — The drum armature winding in 
course of completion is shown in perspective diagram in Fig. 
145. When completed a wire will pass around the cylindrical 
core in one continuous circuit. From symmetrical points leads 
are connected to the commutator bars. When such an armature 
rotates in a two-pole field of force, it will impress electromotive 
force upon a circuit connected to fixed brushes, two in number, 
bearing against the commutator surface at points 180° distant 
from each other and at approximately right angles to the diame- 




FiG. 144.— Twenty-four- Conductor, 

FouB-PoiiE Drum Armature, 

Lap Winding. 



242 



ELECTRICIANS' HANDY BOOK. 



ter connecting the center of the poles of the field magnet. The 
system may be followed out on the leads connected to the com- 
mutator bars, d, e, and f. The rest is incomplete, but the con- 
tinuity of the winding is shown in the part mentioned. Some- 




Ptg. 145.— Drtjm Abmatijrb tn Process of Winbikg. 

times wooden peg« are driven into slots in the core to keep the 
winding in place while being put on, as shown in Fig. 146. 
Another diagram illustrating drum armature winding is given 
in Pig. 147. The heavy black line represents one turn of the 
armature winding, fastened at one end to its proper commuta- 




^^^- 



^M->^ 



Pig. 146.— Operation of Winding a Drum Armature. 

tor division. From the same division a second turn starts, and 
going around the drum connects to the next commutator division. 
The two diagrams illustrate the general lines on which drum 
armatures are wound. 



DIRECT-CURRENT ARMATURE WINDING. 



243 



General Considerations in Laying Out Drum Armature 
Windings for direct-current generation admit of no final descrip- 
tion, because such windings can be executed in many different 
ways. A simple method of doing it, which follows the lines of what 
has been already described, is the following: The number of 
poles in the field must be known. Usually these are of even 
number and in pairs of north and south poles, the two alternat- 
ing with each other. The number of layers of wire to be carried 
by the core is to be settled, and finally the number of commuta- 
tor bars. The controlling factor in settling the last factor is 
the total voltage. This divided by the number of bars gives the 
voltage between adjacent bars. The lower this is kept, the les« 







/'! 



147.— Conductors on a Drum Armature. 



danger will there be of sparking or arcing on the commutator. 
Another point to be kept in mind is that an increase of armature 
divisions, other things being equal, produces a more even electro- 
motive force and current. 

Single Layer Winding for Bipolar Field.— If the winding of 
the armature is based on single active conductors, there must 
be twice as many of them as there are bars in the commutator. 
But for each such conductor any number of leads of wire may 
be substituted. The windings, whether in one or several layers, 
must be divided into twice as many sections as there are divi- 
sions in the commutator. By section, as will be seen later, is 
meant a group of wires lying side by side on the armature 
periphery. Each such division forms a portion of a continuous 



244 ELECTRICIANS' HANDY BOOK. 

coil wound around the core along its periphery and over its 
ends. 

Each such coil will leave two ends. These are connected each 
to its own commutator bar. 

Suppose that there are to be thirty-two divisions in the com- 
mutator; there must then be at the least sixty-four active con- 
ductors on the cylindrical surface of the core. There may be 
substituted for a pair of single conductors connected across -the 
ends of the core a coil of any number of wires, whose free ends 
are treated as are the ends oi a single conductor in the simple 
case of sixty-four conductors. Suppose that there are two poles 
in the field. Then 180° is the controlling factor. 

A circle is drawn to represent the end view or cross section 
of the cylindrical armature core. Around this circle represent- 
ing the core section sixty-four points or little circles are drawn, 
evenly spaced from one another. These represent the end view 
of the sixty-four conductors or groups of conductors. The 
points or little circles are numbered consecutively. Starting 
trom circle number 1, a full line is drawn across the large circle 
to circle number 32 or 34. Either one of these is one removed 
from the 180° position, which latter is held by conductor number 
S3. Suppose number 32 has been selected. From it a dotted line 
is drawn to number 63. This is also one less than 180°, being two 
points distant from point 1, and removed one point from 180". 
Then from 63 draw a full line to a point removed by two points 
from point 32 and removed by one point from 180°. This is point 
30. The same process is kept up until the line drawn from point 34 
to point 1 closes the circuit, and makes the winding re-entrant. 

Double-Layer Winding for Bipolar Field. — Suppose that 
there are sixty-four conductors as before, but arranged in two 
superimposed layers. Tlie circumference of the circle is divided 
into thirty-two parts, and sixty-four points are distributed 
around it in two concentric circles, each containing thirty-two 
points. The inner circle of points is numbered from 1 to 32, 
and the outer circle of points from 33 to 64. Starting from num- 
ber 1, a full line is drawn from it to number 16, and a dotted 
line from number 16 to number 31, and this is continued until 
all but one of the inner circle is connected and number 18 is 



DIRECT-CURRENT ARMATURE WINDING. 245 

reached by a full line drawn from number 3. The inner circle 
of conductors could now be closed and made re-entrant by con- 
necting number 18 to number 1. This is the only open portion 
left. But this would leave out the outer layer of conductors. 
Accordingly, number 18 is connected by a dotted line to number 
33 on the outer layer. A full line connects number 33 to number 
48, a dotted line connects number 48 to number 63, and eventually 
all is closed and made re-entrant by connecting number 50 to 
number 1 of the inner layer. 

The object of drawing some lines dotted and others full is 
simply to distinguish between the ends of the core. The doited 
lines cross one end, the full lines cross the other. 

Commutator Connections. — Every cross connecting wire on 
one end of the core must be connected to a commutator bar. 
Taking the full lines for the crossings on the commutator end, 
each of these must connect to a commutator bar. If Figs. 143, 
144, and others are referred to, the connection to commutator 
bars will be found indicated in them. The windings of the inner 
layer connect to alternate commutator bars, 16 in number; the 
windings of the outer layer connect to the remaining alternate 
bars. 

ilultipolar Windings. — These may be laid out by the method 
given for bipolar windings, except that the controlling angular 
distance is 90° instead of 180°. Suppose a thirty-two-section 
armature is to be connected for a four-pole field. The conductors 
are drawn as dots or little circles around a circle as before and 
numbered. Starting from number 1, it is connected to a con- 
ductor one less or one more than required for 90°, say to num- 
ber 8, by a full line. Number 8 by a dotted line is connected to 
number 15, number 15 by a full line to number 22, and thus 
the process is kept up until a dotted line from number 26 to 
number 1 closes the armature and makes it re-entrant. This is 
a single-layer wave winding. Suppose that as before we had two 
layers, each of thirty-two conductors. Then when number 26 
v/as reached on the inner layer, precisely as above, a dotted line 
would connect it to number 33, a full line would connect number 
33 to number 40, and so on until number 58 would be reached 
by a full line from number 51; then a dotted line from number 



246 ELECTRICIANS' HANDY BOOK. 

58 to number 1 would close the winding and leave it re-entrant. 
The commutator connections are made substantially as described 
above. 

Multipolar Lap Windings. — The last three examples progress 
evenly, and are therefore wave, windings. To make them lap 
windings, conductor number 1 should connect with a conductor 
more than 90° distant, and this last conductor should go back 
in its connections toward number 1, Thus, taking a thirty-two- 
section four-pole winding, number 1 may connect by full line to 
number 10, this by dotted line to number 3, this by full line to 
number 12, and so on .until the armature is closed by a dotted 
line from number 8 to number 1. This system makes the wind- 
ing a lap winding whose net progression is two conductors in- 
stead of seven, as in the wave winding just described. 

Variations on the above are innumerable. The controlling 
angular distance has here been taken as one conductor more or 
less than 180° or 90°. But other distances can be taken. The 
absolutely essential feature is that conductors directly con^ 
ne'2ted must be acted on simultaneously by opposite poles. 

Nomenclature for Drum Armature Windings. — A single turn 
of conductor comprising two peripheral conductors and the con- 
nections across the end of the core of a drum armature may have 
its front ends connected to two adjacent commmtator bars. A 
coil of many turns of wire may occupy the same place, and have 
its front ends connected to two adjacent commutator bars. 
Either of these portions of a winding are called "elements." 
The active portions of an element lie on the cylindrical or periph- 
eral portion of the core, one for one pole and the other for the 
other pole, and are called "sections." In connecting one "sec- 
tion" to another, so as to form an "element," a definite number 
of sections are bridged over or are caused to intervene be- 
tween the sections of an element. A sixty-four-conductor wind- 
ing under this nomenclature is a sixty-four-section or a thirty- 
two-element winding. In the sixty-four-section winding de- 
scribed on page 244 the distance from number 1 to number 32, 
which is a bridging of 32 — 1 or 31 sections, is called the 
"spacing," and it is a spacing of 31 sections. 

General Formulas.— For a bipolar winding we start from one 



DIRECT-CURRENT ARMATURE WINDING. 247 

of the ends of section 1. The cross wire is taken across the end 
of the core to a section a little more or a little less than 180° 
removed from it. If there are four poles in the field for 180°, 
there must be substituted 90°, if six poles 60° must be substi- 
tuted, and so on. These controlling angles are equal to the 
quotient given by 360° divided by the number of poles in the 
field. 

Taking a sixteen-section two-pole winding, it would have in- 
cluded 180°, had the cross wire gone from conductor 1 to con- 
ductor 9. Therefore, the wire may be taken to conductor 8 or 
conductor 10, one being 157°, the other 202° distant in angular 
measurement from conductor 1. 

Bipolar Winding Formula.— Denoting the total number of con- 
ductors on the cylindrical surface of the armature by Z, and 
the number in one element by h, Z/6 is equal to the number of 
elements in the winding; and the number of sections, being two 

in each element, is equal to ~£^and is denoted by s. 

b 
Let the spacing be denoted by y in the cases cited above. The 
general expression for spacing is 

Z 

y= — ± a, 

o 

in which a is any number compatible with tho requirements of 
re-entrant winding and the production of series connection 
through the winding. 

For _ in the last formula we may substitute _^ because 
b 2 

s = Z-£ , and therefore A. =^, and the formula becomes: 
b 2 b 

i5ipolar Winding by Formula. — To put a continuous re-entrant 
winding on a bipolar drum armature on these lines, s must be 
prime to y. If s and y have a common factor, the armature 
winding will have parallel re-entrant coils equal in number to 
tills factor. 

Thus assume s = 16, giving a sixteen-section winding with 



248 ELECTRICIANS' HANDY BOOK. 

eight armature bars. Let p represent the number of pairs of 
poles in the field. Let a = 1, and if the winding is bipolar, 

y 

it follows that p = 1. - r= half the sections or 8. In the 

b 

equation y = y\T^)^ ^^ 

By substituting for p and a their values, each being equal to one, 

and for _— its value, or 8, we have: 
b 

i/ = 8 ± 1 = 7 and 9. 

The one value of s which is 16 is prime to either of these 
values of y, so this winding will be re-entrant in one continuous 
coil. 

The values s r=r 16 and ?/ = 6 or 10, which would result from 
making a = ± 2, are not prime to each other, because they have 
a common factor 2. It follows therefore that this spacing would 
give two re-entrant windings, parallel to each other. 

Multipolar Winding by Formula.— There is no difference in 
general principles between bipolar and multipolar windings. 
Taking the four-pole winding described on page 245, the angular 
distance between sections is 78%°, where in the sixteen-section 
bipolar winding the distance was 157 or 2023^°. 

The general formula just deduced can be made to apply to a 
winding for a multipolar field. Denote the number of pairs of 
poles, which is half the number of single poles, by p. Denote 
the spacing by y. The value of y is then given by the formula: 



Suppose a four-pole armature with thirty-two sections. Then 
p =z 2 and s = 32, and letting a equal 1, we have for the spacing: 



The equation: 



1 / z \ W ^ \ 

armature w 
letting a eqi 

1 f s ^ s 



i 1 = 7 or 9. 



may be transformed to read: 

s=:z2py ± a. 



DIRECT-CURRENT ARMATURE WINDING. 249 

This formula may be used to deduce the number of sections. 

Assume that a four-pole winding is to have about sixteen sec- 
tions; the spacing y will be about 16/4 or 4; and p, which is 
the number of pairs of poles, is 2. Substituting these values i" 
the last equation, it becomes: 

s = 2 (2X 4) ± 1 = 15 or 17. 

This method is only of interest for windings of many sections. 
For ordinary purposes a simpler plan is to take a number of 
sections divisible by the number of poles. Then select for the 
spacing a number one or two greater or less than one-quarter of 
the sections, remembering that it must be prime to the total 
number of sections, and without a common factor if for series 
winding. 

Thus assume a four-pole armature; 24 is divisible by 4, and 
will answer for the total number of sections, s. We have then 

s = 24, 2) = 2, and y =: _J:Z_ ± a. Wie may try for a the 

3X2 

24 
values 1 and 2. The formula then becomes y = ^-— ± 1, or 

± 2 = 4, 5, 7, or 8. Of these, 5 and 7 are prime to 24, having no 
common factor. A spacing of 5 or 7 on a thirty-two four-pole 
winding will be in series and re-entrant. This v/inding with a 
spacing of 7 is described on page 245. 

Lap Winding.— In bipolar and multipolar lap winding we have 
a net value for y. We have to go forward a distance equal 
approximately to the distance between the contiguous pole cen- 
ters, and then to go back a lesser distance, leaving a net spacing 
equal to the difference between the two distances. This net 
spacing is equal to the algebraic sum or arithmetical difference 
of the two. 

It is an object to have the commutator bars even in number. 
To do this the number of sections must be divisible by 4. Thus, 
a fourteen-section or eighteen-section winding would give a 
commutator of seven leaves or nine leaves. 



CHAPTER XIII. 

THE DIRECT-CURRENT GENERATOR. 

The Magneto Generator. — This is a generator in which the 
field is produced by one or more permanent magnets. Fig. 148 

shows a bipolar generator in dia- 
gram. Very large machines have 
been constructed with permanent 
magnets for the field. The cut, 
Fig. 149, shows the De Meritens 
machine, used for the proc^uction 
of the arc light, and the relation 
of field poles to armature coils is 
shown in the small diagram on 
the left, Fig. 150. 

The Modern Multipolar Dyna= 
mo has its yokes contained in and 
forming parts of a species of frame 
of iron. This is a circle or poly- 
gon. From its inner periphery 
cores, one for each pole, project 
toward the center like incomplete 
radii. The ends of the cores cut 
to the periphery of a smaller circle 
form or define the armature cham- 
ber or tube. 

A drum or pole armature ro- 
tates in the space between the 
poles. One brush for each pole 
is typical. From these brushes 
one or more circuits may be supplied. The position of the drum, 
as it is acted on by the radial pulls of the symmetrically placed 




Fig. 148.— Bipolar Magneto 
Generator. 



li 



THE DIRECT-CURRENT GENERATOR. 



251 




cores, tends to hold a central position, which is correct. The 

virtually circular frame 

subjected to radial pull 

alone is exceedingly 

strong, and the magnetic 

pull cannot deform it. 

There is no question of 
the material of the foun- 
dation, for nothing more 
than a magnet yoke, and 
perhaps not even that, 
comes in contact with the 
foundation. 

To the mechanic's eye 
the symmetry of the 
multipolar machine is 
attractive. The project- 
ing pole pieces are short 
and thick, so as to mini- 
mize leakage of lines of yiq. U9.-DeMeritens Magneto Generator. 
force. The rotating part 

of the machine, the commutator and the brushes, are at a distance 

from the floor, and less liahle to 
pick up dirt than in the old type 
of machine. 

The poles may be of any num- 
ber, limited only by practical 
considerations. For direct cur- 
rent work relatively heavy cur- 
rents as a rule are generated, so 
that the necessity of using thick 
wire tends to limit the number 
of poles. 

The construction is symmetri- 
cal, and the field sections may 
be made on the interchangeable 
plan, even if some special planing is needed to bring them smooth- 
ly into place in setting up a machine. But the construction is 
so strong that there is never any need of replacing field sections. 




Fig. 15\— REiiATiON of Armature 
Coils and Field. 



252 ELECTRICIANS' HANDY BOOK. 

Advantages of flultlpolar Construction.— The old type of 
two-pole dynamo with parallel magnet legs has been abandoned 
generally for the multipolar type. The objections to the bipolar 
type are as follows: 

To take the drag of the heavy armature off the bearings, the 
armature end of the magnet has to be placed downward. The 
magnetic pull tends to lift the armature from the bearings and 
make it run easily and prevent wear of the under journal-box. 
But the placing of the armature end downward makes it impos- 
sible to use an iron base for the machine. Such would short- 
circuit the lines of force, and would thereby weaken the field 
of force in which the armature rotates. 

The long magnet legs give much magnetic leakage, as shown 
in Fig. 81, page 184, thus further weakening the field. Never- 
theless, good results were reached with the old-time bipolar 
dynamos. 

Field Winding of Dynamos. — The general principle upon 
which the field magnets of dynamos and motors are wound is ex- 
ceedingly simple, and is what has been described under electro- 
magnets. Each pole piece has in the typical and almost" univer- 
sal class of machines to be of opposite polarity to its neighbor. 
The windings, if directly on the pole pieces, follow the rule of 
electro-magnet winding, so that the current around the south 
poles follows the direction of motion of the hands of a watch if 
the pole is facing the observer, and the reverse holds for the 
north pole. The windings in a bipolar magnet if on the legs 
compare exactly with those of an ordinary electro-magnet. The 
wire crosses from the front of one leg to the rear of the other, 
so as to give one north and one south pole. 

A single winding on the yoke connecting the legs is sometimes 
used for both poles. 

On multipolar machines with windings on the poles, the same 
rule is followed as for bipolar windings, the wire crossing from 
front to rear of the pole pieces adjacent to each other. 

Series Winding.— The simplest or most natural conception of 
a dynamo is the series-wound dynamo. In it the terminals of the 
armature are connected as follows: One is connected to one end 
of the field winding. The other is connected to the end of the 



THE DIRECT-CURRENT GENERATOR. 



253 



outer circuit. The other end of the outer circuit is connected to 
the remaining field terminal. The cut, Fig, 151, shows a diagram 
of a bipolar series dynamo, and Fig. 152 shows the same in con- 
ventional diagram. 

This type of connection is of almost historical interest. It is 
impossible not to recognize in it the foundation of the modern 
dynamo. The self-exciting dynamo, relatively small in size, had 
no difficulty in replacing the old magnetos. It must not be for- 
gotten that powerful magnetos 
were constructed in old times, 
and were used for lighthouse il- 
lumination. 























i 




' L * 




1 — ^^ 




[■©•J 



M 




Fig. 151.— Series- Wouxd 
Dynamo. 



Fig. 153 — Conventional Representa 
TiON OF A Series- Wound Dynamo. 



But when the self-excited dynamo appeared on the scene, with 
a field enormously intensified over that of the old magneto; a 
veritable revolution was made. The modern engineer often winds 
his fields in parallel with the outer circuit, or has them wound 
with two coils part in parallel and part in series. He may use a 
small independent machine to excite the field, which also is an 
old idea, so that the principal machine has only its armature 
coils traversed by the current it produces. Yet the self-exciting 
series-wound dynamo must be regarded as one of the parents in 
the already long line of ancestors. 

The winding is seen to be adapted to produce opposite polarity 
of adjacent poles. 



254 ELECTRICIANS' HANDY BOOK. 

Action of Series Winding.— The action of series winding brings 
about several conditions. The armature can generate no elec- 
tromotive force until the field is excited by the current this 
electromotive force produces. Therefore to start it everything 
must be done to favor the production of current. The dynamo 
is best started on very low external resistance, and the armature 
may have to be speeded up. To facilitate starting, it is impor- 
tant to have good permeance, or to have a good magnetic circuit. 

The polarity of the machine is fixed by the polarity of the field 
magnet poles. As shown in the cut, the direction of the cur- 
rent is indicated by the arrows. But if for any reason the dyna- 
mo began self-excitation or building-up with the north and south 
poles reversed, the current would flow in the other direction. This 
happens not infrequently with series-wound machines. For elec- 
tric light this may or may not be of importance; for charging 
storage batteries or electro-plating it is imperative that no change 
occur. 

If the resistance of the outer circuit is increased, the electro- 
motive force diminishes. If the same resistance is diminished, 
the electromotive force increases. These two effects are due 
to the effect of resistance on the total current which passes 
through the field magnet coils. 

If used for constant-current lighting, the addition of a lamp 
will cut down the electromotive force exactly when it is most 
needed. If used on parallel-circuit lighting, each new lamp light- 
ed will cut down the external resistance, strengthen the field, and 
increase the electromotive force. This involves danger of burn- 
ing out the lamps. 

Series winding therefore has its defects, and the tendency is to 
adopt other windings. 

Shunt Winding.— A shunt-wound dynamo is one whose field 
magnets are wound in parallel with the outer circuit. The ter- 
minals of the armature winding, which are the brushes, are con- 
nected each to two wires. One is a terminal of the outer circuit, 
the other a terminal of the field-magnet winding. 

The cut, Pig. 153, shows a bipolar dynamo shunt-wound. Fig. 
154 shows a conventional representation of the same. It will 
be seen that the potential difference or voltage expended in the 



THE DIRECT-CURRENT GENERATOR. 



255 



field magnet and outer circuit are identical. The energy expended 
on the field magnet is totally lost as far as any economic effect 
is concerned. It is of importance to keep its value as low as 
possible. The volts are fixed and beyond control. The only way 
of reducing the watts of energy expended in the field is to re- 
duce the amperes. Accordingly, the winding of a shunt dynamo 

is of fine wire and of many turns. 
This causes it to carry only a 
small proportion of the total cur- 
rent. The watts absorbed by it, 
as the volts are relatively con- 
stant, is directly proportional to 














i 


"S-^ < 


' 






; < 





i_ 






1^ 


/ 




Fig. 153.— Shunt Wound. 



Fig. 154.— Conventional Eepresent^ ■ 
TiON OF Shunt Winding. 



the amperes of current which pass through it. By this way of 
winding the field coils the proportion of energy expended on 
their excitation is kept as low as in the series-wound machines. 

Action of Shunt Winding. — The action of a shunt-wound dy- 
namo is the reverse of that of a series-wound one. 

If the resistance of the outer circuit is increased, the field mag- 
net receives more current, and the voltage at the armature ter- 
minals increases. The effect is that produced in the series ma- 
chine by short-circuiting. 

If a shunt-wound machine is supplying lamps operated in par- 
allel, the resistance of its outer circuit will be decreased as more 
and more lamps are operated. This causes less current to be 
shunted into the field, and the voltage falls. 



256 ELECTRICIANS' HANDY BOOK. 

The effect of taking current from the field reduces its mag- 
netization. This in its turn reduces the electromotive force 
generated by the armature. This reduction comes in as a third 
step, and again cuts down the field current. Nevertheless, some 
shunt dynamos with low-resistance armatures regulate them- 
selves fairly well within a reasonable limit of action. 

If the resistance of the outer circuit is raised, the intensity 
of magnetization is increased, as more current is shunted around 
the field, 

A shunt-wound dynamo may supply a constant-current system 
of lamps very well. This is the system where the lamps are in 
series. If new lamps are added to the series, the resistance of 
the outer circuit is increased, more current is shunted through 
the field coils, and the electromotive force and voltage of the 
outer circuit increase. This is in the direction of meeting tho 
greater demand for potential. 

The series machine, because of its connection, must have th£ 
full current pass through its windings. This current cannot be 
changed. The current passing through the field windings in the 
shunt machine can be varied. This may be done by placing a 
variable resistance in circuit with the field windings. By in- 
creasing this the field is weakened and vice versa. 

Compound Winding.— A dynamo consisting of a combination 
of the series and shunt machines is called a compound-wound 
dynamo. 

The field magnet is encircled by two windings. One is a pro- 
longation of the outer circuit, exactly as in the series dynamo. 
The other is a finer wire circuit, in parallel with the outer cir- 
cuit, exactly as in the shunt-wound dynamo. 

Of the compound-wound machines, there are two variations 
shown in the diagrammatic cuts, Figs. 155, 156, 157 and 158. 

Short=Shunt Compound Winding.— The first variation, Figs. 
155 and 157, is the short-shunt machine. The shunt field circuit is 
connected directly to the brush terminals. The outer circuit, with 
the series field circuit in series with it, is connected to the same 
terminals. The shunt field coil is in parallel with the line, con- 
taining outer circuit and series magnetizing or field coils. 

Long=Shunt Compound Winding.— The second variation, Figs, 



THE DIRECT-CURRENT GENERATOR. 



257 



156 and 158, is the long-shunt machine. In this only one ter- 
minal of the shunt coil is connected directly to a brush terminal. 
The other end of the shunt CQ^il connects to the outer circuit be- 
yond the outer end of the series field coil. In this connection 
the shunt coil is in series with the armature and outer circuit 
and in parallel with the series coil. 

Action of Short=Shunt and Long=Shunt Windings. — There is 
not much difference in the action of these two kinds of windings. 





Fig. 155.— Compound- Wound 
Dynamo, Short-Shunt. 



Fig. 156.— Compound- Wound 
Dtnamo, Long-Shunt. 



In the short-shunt winding an identical current goes through the 
shunt as long as the same voltage is maintained at the armature 
terminals or brushes, because the shunt coil takes its current 
from those terminals. In the long-shunt winding there is a 
slight variation in the voltage of the shunt coil, with constant 
voltage at the brushes, if there are variations in the current 
in the outer circuit. 

Self = Regulation of Compound- Wound Dynamos.— If a com- 
pound-wound dynamo is supplying a circuit at constant poten- 
tial, it may be almost self-regulating. Suppose the resistance 
of the outer circuit to be diminished. This sends more cur- 



258 



ELECTRICIANS' HANDY BOOK. 




Fig. 157.— CONVENTioNAii Representa- 
tion OF Short-Shunt Dynamo. 



rent through the series coil, and thereby acts to increase the 
intensity of the field. But the reduction of resistance in the 
outer circuit reduces the current in the shunt winding. This 

action goes to reduce the 
intensity of the field. 
By giving proper propor- 
tions to the two exciting 
coils, the intensity of the 
field can be kept prac- 
tically constant as the 
resistance of the outer 
circuit is increased or 
diminished. The arma- 
ture being kept at a con- 
stant speed of rotation in 
a constant field of force 
by the engine or other 
source of mechanical 
power, impresses on the 
circuit the identical elec- 
tromotive force. As its 
resistance and that of 
the series field coil is 
constant, the voltage at 
the terminals remains 
constant. 

This applies to an ac- 
curately arranged wind- 
ing. Whether the result 
is reached by calculation 
or by trial, it can be attained very closely. At high or low cur- 
rent strength there is apt to be a comparatively slight change in 
voltage. 

Characteristic Curves.— On page 283 are given characteristic 
curves of series-wound and shunt dynamos. If it is realized 
that the characteristic of a compound-wound machine may be 
almost a horizontal line, its self-regulating powers will be seen. 
This appears from Figs. 176, 177 and 178. 




Fig. 158. - Conventional. Representation 
OF Long-Shunt Dynamo. 



THE DIRECT-CURRENT GENERATOR. 259 

Over=Compounding. — The result of such even action as de- 
scribed above is the maintenance of constant voltage at the termin- 
als of the machine. In electrical work all sorts of conditions may 
have to be met. A very usual one is that on a circuit a constant 
voltage is required, not at the generating plant, but in the heart 
of the district, perhaps miles away. 

In an over-compounded dynamo the series coil is given so 
many turns in proportion to the turns in the high resistance 
shunt coil that its influence overbalances that of the shunt coil. 

The effect of over-compounding is to cause the voltage at the 
terminals of the machine to rise with increase of current. The 
proportional increase of voltage with increase of current can be 
accurately regulated by the relative sizes of the coils. It is only 
necessary to follow what has been said of the series dynamo, and 
to regard the compound-wound machine as a series dynamo 
greatly reduced in its characteristic action. 

Over-compounding enables a constant voltage to be maintained 
in any point of a district. The resistance of the mains between 
the dynamo in the station and the given point in the district is 
known. The drop in voltage due to that resistance varies with 
the current. The over-compounding of the machine can be regu- 
lated to give the same increase in voltage with the increase of 
current, and thus the voltage at any desired point in the district 
can be kept constant, following Ohm's law. 

Example of Compound Winding Calculation. — Suppose the re- 
sistance of a single lead of the mains to be 0.01 ohm. Then that 
of the two leads is 0.02 ohm. Suppose a maximum current of 
500 amperes is needed. The drop due to the specified resistance 
and current is obtained by Ohm's law: 

RI = E 

or 0.2 X 500 = 10.0 volts. 

This of course is an extreme case. But the dynamo by over- 
compounding cs,n be made to vary its voltage at the terminals in 
this or any other desired proportion to the current. With the 
resistance given above, and the variation in voltage for the cur- 
rent as calculated above, which variation is at the terminals, 
a constant voltage would persist at the outer end of the leads. 



260 ELECTRICIANS' HANDY BOOK. 

Excitation of Field Coils in Compound Dynamos. — The series 
field coils of dynamos can only be excited by the working cur- 
rent or by a portion of it. If the machine is compoimd-woimd, 
the series coils are taken care of by the machine. The shunt 
coils may receive their current from various sources. To make 
the machine self-regulating, it would seem that the shunt coil 
should be fed from the machine proper. This practice makes tlie 
dynamo self-contained. 

Two other systems of shunt-coil excitation are used. In one 
system the terminals of the shunt coil are connected to the leads 
or bus-bars of the main circuit; in the other, a separate source 
of current is used for the shunt coils. When several dynamos are 
operated, and constant potential is maintained in the circuit at 
all times, a new element in the magnetization of the field is in- 
troduced because the magnetization, as far as the shunt coil is 
concerned, in this arrangement is independent of the speed of 
the dynamo. The excitation becomes zero when a self-exciting 
dynamo stops. 

Effect of Independent Excitation of Shunt Coil. — If the ter- 
minals of the shunt coils are connected to an always active outer 
circuit, to station bus-bars for instance, the shunt coil excites the 
field as long as the connection is kept closed. As the dynamo 
runs slower the field excitation diminishes, but with less rapidity 
than before, and is never reduced to zero until the bus-bar or 
main circuit connection is broken. It is a case of under-com- 
pounding. The great advantage of it is that it makes it possible 
to excite the field before starting a dynamo. The field before 
the armature begins to rotate is not only excited, but the correct 
polarity is established. The instant the dynamo begins to work, 
electromotive force is impressed upon the armature coils, and 
there is no difficulty in bringing the voltage up to that of the 
main circuit. 

Disconnecting or Opening the Shunt Coil. — The capacity of 
the shunt coil is considerable. It cannot with safety be dis- 
connected by a simple opening of a switch. A bank of lamps 
is generally mounted in series with it. The field break switch 
is placed between the lamps and the main circuit. When it is 
opened, the resistance of the lamps prevents undue sparking. 



THE DIRECT-CURRENT GENERATOR. 



261 



^>^ 



Separate Excitation of Shunt Coil.— The shunt coil may also 
be excited by an independent source of electric energy. This 
may be a storage battery or an exciting dynamo. The separate 
excitation brings about a particular result. The exciting ma- 
chine will be run at a constant voltage, so that the current 
passed through a separately excited shunt coil can be absolutely 
constant. The inevitable variations in voltage on the outer 
circuit bring about some variation in current in shunt coils fed 

from the bus-bars, which 
variation may be slight, 
but it exists. Otherwise, 
the result of separate 
excitation is not to be 
distinguished from outer 
circuit or bus-bar exci- 
tation. It gives another 
dynamo or storage bat- 
tery to be looked after. 

Exciting Series Coils 
from Main Circuit. — A 
very obvious way of ex- 
citing the field coils of a 
compound dynamo is to 
send current through its 
series coils from the 
main circuit. This is 
done by closing two 
switches, one connecting 
a terminal of the field series-coil with one lead of the main circuit, 
and the other connecting the other end of the same coil with an 
equalizing bar or by special connection with the other main-circuit 
lead. This leaves the armature for the moment out of circuit. 
The dynamo can then be started and brought up to the proper 
potential. The armature has electromotive force impressed on it 
at once, and excites the shunt coil. Thus it is brought with cer- 
tainty into action, and the polarity is fixed from the start. 

Separately = Excited Generators. — The separately-excited dyna- 
mo closely approaches the magneto in its action, as the strength 




"Pig. 159.— Separatelt-Excited 



262 



ELECTRICIAN ti' HAl^DY BOOK. 



of the field does not directly depend upon the current generated. 
The diagram, Fig. 159a, shows the connections for the separ- 
ately-excited machine. The field-magnet coils are entirely separ- 
ated from the commutator connections. A current passing through 
the coils produces a field of definite and irreversible polarity. 
The armature rotates in the field, and impresses electromotive 
force of definite polarity on the circuit. 

The current which excites the field magnet may be derived from 
a small dynamo, or from any source desired. 

Action of the Separately=Excited Dynamo. — This arrangement 
has several advantages. The absolute irreversibility of polarity 
may be a very valuable feature. Thus, when storage batteries are 

being charged with a self- 
excited machine, the polarity 
sometimes becomes reversed. 
\ja. such a case, if there is 
any charge in the battery, 
it discharges through the 
dynamo, and the latter be- 
comes a motor, and the 
charge is wasted and lost. 
A similar trouble occurs in 
electroplating. 

But with separately-excit- 
ed machines this class of trouble is impossible. If its voltage 
is insufficient to fully charge a battery, it will at any rate not act 
as a motor and discharge what may be in the battery. The electro- 
plater is c-ertain that with a separately-excited dynamo his articles 
in the plating bath will receive the desired deposit and will not 
strip and lose what they have received. 

Regulation of Separately = Excited Dynamos and Magnetos.— 
There are three general factors of regulation of magnetos and 
separately-excited generators. 

The speed of rotation of the armature may be altered. This 
changes the lines of force cut in a given period. 10^ lines of 
force cut per second, it will be remembered, gives one volt. 

The brushes may be pushed forward on the commutator. This 
introduces demagnetizing turns in proportion to the advance of 




Fig. 159a.— Rheostat for Regulating 
Sepabatelt-Excited Dynamo. 



THE DIRECT-CURRENT GENERATOR. 



263 



the brushes. This is described in Chapter XIV. Thus the mag- 
netic circuit, although produced by separate excitation, can be 
reduced by self-regulation. 

Another way is to change the normal magnetic flux through the 
armature by outside means. An old device with magnetos was 
to provide a movable piece of iron, which could be moved toward 
or away from the poles of the magnet. This as it approached 
the poles shunted off more and more of the lines of force from 




Fig. 160.— Separate-Cibcutt 
Dynamo. 



Fig. 161,— Skparately and Self- 
Exciting Series Dynamo. 



the armature, weakening the field and reducing the electromo- 
tive force. In separately-excited machines the current passing 
through the field-magnet coils can be weakened by the introduc- 
tion of resistance into the exciting circuit, or by any other means. 
A rheostat-like arrangement can be introduced to cut out some 
of the coils of the field, as shown in Fig. 159a, in which R denotes 
the rheostat. 

The Separa$e= Circuit Dynamo has either two separate arma- 
tures in the field space, or has two sets of coils. Whichever 
it is, one armature or coil set is used to excite the field, the 
other to supply the current to the circuit. Fig. 160 shows a 



264 ELECTRICIANS' HANDY BOOK. 

diagram of such a dynamo with two commutators, from one of 
which the field current, and from the other of which the field 
magnet current is taken. 

Separately and SeIf=Excited Dy name— The diagram, Fig. 
161, shows this machine, in which a current from an outside 
source passes through one field coil, and the main current of 
the dynamo passes through a second field coil. 

Multipolar Dynamo Connections. — To avoid complication and 
to give diagrams readily understood, only two-pole machines have 
been illustrated in this chapter. But everything which has been 
shown for such machines applies to multipolar machines. The 
conventional diagrams may be used for multipolar machines ex- 
actly as employed in this chapter. The few turns of wire indi- 
cated may refer to the winding of any number of poles. 

Conventional Representations of Machines, — The tendency 
of engineers is to simplify their diagrams as much as possible 
and to indicate a machine with numerous poles by a few lines 
only, as if it were of the simplest construction. Except for small 
machines the bipolar construction may be considered to be de- 
finitely abandoned, as is explained elsewhere. The brushes are 
conventionally drawn as if they were set tangentially. This is 
done for a purpose, as it serves to indicate the direction of rota- 
tion of a machine. Often this is not essential as far as the draw- 
ing is concerned, and the brushes may be shown as radial brushes 
or lines, as in Pig. 159a. 

Later the representation of an alternating-current machine will 
be spoken of, and it will be seen that the distinction between the 
direct-current and alternating-current machine depends upon the 
representation of the brushes. 

In these conventional figures those remain in use which 
are the simplest and most effective as regards freedom from 
misunderstanding. 



CHAPTER XIV. 

ARMATURE REACTIONS. 

Armature Polarity Due to Its Windings. — The armature of a 
direct-current dynamo, by the polarity it acquires from its wind- 
ings, modifies the course of the lines of force. If the dynamo is 
idle or on open circuit, no current passes through the armature, 
and any lines of force which may exist go straight across from 
field magnet poles to the armature core. 

But the current which goes through the windings of a dynamo- 
or motor-armature operates to produce north and south poles in 
it. These are situated at points about equally distant from the 
poles of the field. In a bipolar machine the line connecting the 
north and south poles of the field is approximately or exactly at 
right angles to the line connecting the north and south poles of 
the armature core. 

Action of Field Poles on Armature Core.— The field poles 
tend to induce polarity in the parts of the core nearest to them, 
the north pole inducing south polarity and the south pole north 
polarity. The effect of the combination of polarities, one due to 
the field poles' induction and the other to the induction of the 
armature windings, is to give resultant poles to the armature at 
intermediate points. 

The lines of force emerge from one pole of the field, go 
obliquely to the opposite resultant pole of the armature, obliquely 
through the armature to its opposite corresponding pole, and 
thence obliquely to the adjacent pole of the field. 

Field Distortion. — This armature reaction introduces mani- 
festly an element of complexity into the subject. It is no longer 
a simple set of straight lines of force which constitute the field, 
but an S-shaped volume of polarized ether, constituting a dis- 
torted field of force. 



266 



ELECTRICIANS' HANDY BOOK. 



Armature Reaction Diagrams.— The reaction of the magnet- 
ized armature core is easily understood from an inspection of 
the diagrams. 

The diagram, Fig. 162, shows an idle armature lying between 
two pole pieces of an active field magnet. The wires are indicated 
by circles. Those with crosses show the current going away 
from the observer, those with dots the current approaching; 
those with neither show idle wire. The iron core of the arma- 




(rXiXiX:) 



FiQ. 162.— TJnexcited Armature in Excited Field. 



NN 



cmn 




Fig. 163.— Excited AnMATURE in Unfxcited Field. 



ture has induced in it two poles opposite those of the field mag- 
net, and the general course of the lines of force is indicated by 
dotted lines. 

The diagram. Fig. 163, shows an excited armature between the 
poles of an idle field. There the poles in the armature lie at 



ARMATURE REACTIONS. 267 

right angles to the field pole pieces, and the same conventional 
signs are used for the currents in the wires. The armature poles 
in this figure are at N and S. 

In Fig. 164 both field and armature windings are supposed to be 
passing current. It will be seen that there are four poles, two N 
poles and two S poles, each pair at right angles to the other. 
The S pole of the field tends to establish an N pole in the arma- 
ture core opposite to itself. The N pole of the field tends to 
establish an opposite and corresponding S pole in the armature 
core. The windings of the armature tend to produce their own 
poles on the vertical line as shown. The resultant poles in the 
armature lie between the two pairs. The resultant N pole lies 



S 
FiQ. 164.— Excited Armature in Excited Field. 

in the right-hand upper quadrant; the resultant S pole in the 
left-hand lower quadrant. 

Varying Densities of Field.— Not only are the poles of the 
armature core thus displaced out of symmetry. The lines of 
force are densest in distribution between opposite-named poles 
of the field and armature core. They are crowded together 
toward the horns or ends of the pole pieces that lie in the direc- 
tion of the motion of the armature. They are thinned out at the 
other horns. All this is shown in the cut. This crowding to- 
gether of the lines of force is due to a reaction between the core 
poles and the field poles. This reaction in the case shown in the 
figure tends to displace the S field pole upward and the N field 
pole downward again in the direction of rotation. 

Were there no displacement of poles, the poles of the armature 



268 ELECTRICIANS' HANDY BOOK. 

should lie upon a line at right angles with the line connecting N 
and S poles of the field. In the three figures these poles would 
lie on the vertical line. But owing to the armature reaction, the 
brushes have to be shifted in a dynamo in the direction of the 
rotation. Their line of position is now oblique to the line con- 
necting the centers of the field magnet poles. 

Neutral Points. — The points connected to the brushes are 
termed the neutral iDoints, These normally lie at the ends of the 
oblique diameter described in the last paragraph. 

It is perfectly evident that the armature reaction may vary 
under different conditions of load. Especially is this to be looked 
for in shunt or compound wound dynamos. The neutral points 
vary according to the relative intensities of magnetization of 
field magnets and armature cores. 

Brush Adjustment. —To meet this variation of positions of 
the neutral points, the brushes are mounted on a rocker so as to 
be movable back and forth. They are rigidly connected with 
each other, so as to always be at opposite extremities of a diame- 
ter, but by turning their mounting or "rocker" back and forth, 
their position can be made to coincide with that of the neutral 
point. 

Demagnetizing Turns. — The brushes are advanced from the 
ends of the symmetrical line of the armature through a distance 
which may be stated in terms of an angle of so many degrees. 
If we go back from each brush against the direction of rotation 
a distance equal to twice this angle, we get a space called the 
demagnetizing belt, and the turns of wire comprised in this belt 
are called demagnetizing turns. In the cuts. Figs. 165 and 166, 
the condition is shown, n n' is the line connecting the neutral 
points; a & and c d cover the demagnetizing turns. The same 
conventional signs show the direction of current. It is obvious 
that the demagnetizing belt is working against the field-magnet 
turns, and reducing the intensity of the field of force. The 
brushes should be kept as near the symmetrical points as possi- 
ble. The arrows in Pig. 165 show the general direction of the 
armature currents. 

Reduction of Field Density.— Referring to the same figures, 
the turns outside the demagnetizing belt tend to diminish slightly 



ARMATURE REACTIONS. 



269 



the intensity of field. Tliis is by their action in crowding together 
tlie lines of force at the advanced horns of the field magnet poles. 
This reduces the permeability of the iron at that point, and 
hence reduces the field density or intensity. 

Demagnetizing turns are entirely distinct from the armature 
reactions described on the preceding pages. The turns in the de- 
magnetizing belt are in direction of current the reverse of those 
in the field magnet. 

Action of (he Demagnetizing Turns. — The action of the de- 




FiGS. 165 AND 166.— Neutral Line and Demagnetizing Turns or 
Armature, 



magnetizing turns is to weaken the field. The armature core is 
a part of the magnetic circuit, and whatever affects the lines of 
force which go through it affects the whole circuit. The demag- 
netizing coils have no action except when a current is going 
through them, and their action varies with the intensity of the 
current. It is simply a matter of ampere turns working in 
opposition to the ampere turns of the field. 

The electromotive force of dynamos naturally rises as the speed 
increases. But most series-wound machines reach a maximum, 
and then tend to fall off in electromotive force. It is due in 
great part to the advance of the brushes under increased load. 
This throws more turns of wire into the demagnetizing turns, 
and thereby increases the counter or back ampere turns. The 
distortion of the lines of force has also something to do with this. 



270 



HJLECTRIGIANS' HANDY BOOK. 



Dead Turns. — It follows from the above and from some other 
reactions which may be included, that the increase in electro- 
motive force is not strictly proportional to the speed. Thus, if 
the electromotive force were to be increased ten per cent, it 
might be necessary to increase the revolutions twelve per cent. 
The extra revolutions of the armature required, above the propor- 
tion of the voltage gained, are called "dead turns." 

Spurious Resistance.— Self-induction in a conductor does two 
things. It resists the starting of a new current through a con- 
ductor, and tends to pro- 
T long the passage of an ex- 

isting current if anything 
occurs to diminish it. The 
latter action is what pro- 
duces the spark on open- 
ing the circuit of a spark 
coil. Consulting Fig. 167, 
it will be seen that one 
coil of an armature is 
shown short-circuited by 
one of the brushes. As the 
armature rotates, coil after 
coil is thus short-circuited. 
T and U have just been 
short-circuited, and W and 
X will next be. The self-induction acts to send a current through 
the coil for perhaps only a portion of the exceedingly brief period 
when it is short-circuited. This is a loss of energy. As it passes 
on, a new current has to be started, and is resisted by its self- 
induction. This is another loss of energy. These actions increase 
in degree with the speed, and reduce the current. They act like 
resistance, and the term spurious resistance is applied to them. 
Spurious resistance increases with the speed of rotation. 

Anything which will reduce the inductance of the armature 
will reduce spurious resistance. The fewer turns of wire in the 
armature, the less will the inductance and the spurious resistance 
be. But in designing dynamos and motors, spurious resistance 
is rather a minor consideration. 




Fig. 167.— SHORr-CiRCUiTiNG of an 
Armature Coil, by a Brush. 



ARMATURE REACTIONS. 271 

Eddy or Foucault Currents., — If electromotive force is im- 
pressed upon the windings of an armature, it follows that it will 
also be impressed upon all metal parts of it. The core is not 
only not exempt, but its periphery is subject to nearly as strong 
induction as the coils themselves. Accordingly, currents whose 
direction is determined by the regular laws of induction are pro- 
duced in them. These currents existing within the mass of the 
metal are termed eddy currents or Foucault currents. The por- 
tions of the metal nearest the surface are most impressed with 
electromotive force; the outer portions cut more lines of force 
per revolution than do the inner portions of the core. The elec- 
tromotive force impressed on one side of the core is of opposite 
polarity to that impressed on the other. 

Differential action of electromotive force on a conductor will 
set up currents according to Ohm's law. These make themselves 
known by the heat which they produce in the metal in which 
they are generated. A copper or iron wheel rotated rapidly in 
a strong electric field becomes hot from the generation in it of 
eddy currents. 

Eddy Currents in Armature Cores. — Energy is expended on 
the production of these currents, which is totally lost as far as 
any useful effect is concerned. There is no available way of sup- 
pressing them in armature cores except by a somewhat crude 
method. The core is built up of a quantity of pieces of thin 
iron, insulated from each other, and set at right angles to the 
direction in which the impressed electromotive force tends to 
produce a current. It is called a laminated core. 

A cylindrical armature core is accordingly made of a pile of 
circular disks of thin iron. Between them are placed layers of 
some insulating material, such as paper, and thus the possible 
path of the currents is so much shortened that they amount in 
the aggregate to comparatively little. The object is thoroughly 
attained by making the disks as thin as possible and insulating 
them well. 

Eddy Currents in Core Disks. — Eddy currents are established 
in core disks, though of relatively little importance. The cut. 
Fig. 168, shows how such currents act in laminations. The thick- 
ness of the lamination is greatly exaggerated in the cut. 



272 



ELECTRICIANS' HANDY BOOK. 



Eddy Currents in Pole Pieces.— Any alteration in the distribu- 
tion of the lines of force in the field will cause eddy currents in 
the contiguous masses of metal. Thus, eddy currents may be 
produced in the pole pieces of the field magnet if the iron core 
of the armature is not perfectly cylindrical. Some types of arma- 
ture have projecting teeth of iron, the disks being out of contour 
to give projections. These teeth, as they sweep past the smooth 

circle of the pole pieces, 
virtually carry an intense 
little field of force of their 
own with them, and thus 
start eddy currents in the 
pole pieces. 

Every eddy current rep- 
resents joules of energy, 
and has to be accounted 
for in the power. 

End Leakage of Lines 
of Force in Armature.— 
Lines of force may leak 
around into the flat ends 
of the armature core. These will be enough to start currents 
flowing through these disks. If the armature core extends out 
beyond the pole pieces, this source of eddy currents is disposed of. 
Eddy Currents in Conductors. — If the conductors or windings 
of an armature are very thick, eddy currents may be produced in 
them. This makes them carry several currents, one running 
counter in part of its course to the regular current. 

All eddy currents, representing loss of power or waste of en- 
ergy, must be suppressed as far as possible. The worst ones 
which can be produced are core currents, and these are minim- 
ized by laminating the core. 




Fig. 168.— Eddt Currents in Armature 

Laminations. 



CHAPTER XV. 



CHARACTERISTIC CURVES. 



conditions is represented by 
curves. These are diagrams 



Characteristic Curves. — The action of dynamos under various 

what are known as characteristic 
constructed on the usual basis of 
lines at right angles to 
each other. The vertical 
line may be divided into 
parts representing volts — 
generally the difference of 
potential between the ter- 
minals of the dynamo. The 
horizontal line may be di- 
vided into parts represent- 
ing amperes. The vertical 
and horizontal scales may 
also be given other mean- 
ings. 

Hopkinson, who in 1879 
first proposed this way of 
representing the action of 
a dynamo, used the values 
of the total electromotive 
force for the vertical line. 
Pig. 169 is an example 
of a characteristic cuive, 
E, of a series-wound dyna- 
mo. It shows the electro- 
motive force for small currents increasing much more rapidly 
than it does when the current increases. It is evident that with 
enough current taken out of the machine, the electromotive force 
would remain practically constant. 















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/ 














/ 














/ 















20 



50 



Fig. 



30 

AMPERES 

?,— Characteristic Curve of a 
Series-Wound Dynamo. 



274 



ELECTRICIANS' HANDY BOOK. 



The variations in current are produced with constant speed of 
rotation by changing the external resistance. The internal re- 
sistance remaining constant, and the field excitation varying with 
the current intensity, are two of the controlling factors which 
produce the curve. 

Horse=Power Lines. — Seven hundred and forty-six watts or 
volt-amperes are an electrical horse-power. Points on a charac- 



v»100 








r^7 






V'' 


^ \ 


80 
60 

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SO 
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AMPERES 



Fig. 170.— Horse-Power Lines. 



teristic curve diagram can be determined where the product of 
the volts and amperes is equal to 746. These points joined give 
a one-horse-power curve. Other points are where the product of 
the volts and amperes is equal to 746 X 2 or 1492 watts, which are 
equal to two horse-powers. These points connected give a two- 
horse-power curve. The process is carried out for other horse- 
powers, as shown in Fig. 170. 
The characteristic curve in connection with this set of horse- 



Mi 



CHARACTERISTIC CURVES. 



275 



k 



power curves tells two things. It indicates the relation of 
amperes to volts in a specific machine corresponding to the 
various horse-powers. 

Types of Characteristic Curves. — There are different types of 
characteristic curves. The one just spoken of is referred to the 
electromotive force of the dynamo, and is called a total charac- 
teristic curve. Another 
type of curve is referred to 
the potential difference ex- 
isting between the ter- 
minals of the dynamo. 
This potential is easily de- 
termined by a voltmeter. 
Such a curve is called an 
external characteristic 
curve, or sometimes the 
terminal potential curve. 

Drooping Ciiaracteris- 
tic— In the cut, Fig. 171, 
the internal characteristic 
curve, e, corresponding to 
the external one, E, is 
shown in dotted lines. Be- 
yond a certain point, about 
27 amperes, the voltage be- 
gins to decrease in value. 
A curve of such a shape 
is called a drooping curve. 
Sometimes characteristics 
droop much more than 

this. An advantage attaches to this drooping. It indicates that, 
should the machine be short-circuited while running, the electro- 
motive force will not increase. A machine with drooping charac- 
teristic is advantageous for constant-current arc lighting. 

The straight line J is the characteristic of the armature. The 
curve e is derived from E by subtracting the ordinates of J 
from those of E, and drawing the curve e through the points 
thus determined. 



90 
80 








._. 




^_^ 


-E 






^ 


^ 










/ 


/ 










JQ 




/. 


Z^' 


---> 


-^^^ 






60 

M 

"3 50 
40 




// 




720 F 


!EV. 


^-. 


"•--e 




/ 










\ 


// 
// 










,-''' 




32 


// 






^^'' 


y' 








// 




/-^ 














/' 













10 



20 



50 60 70 



30 40 

AMPERES 

Fig. 171.— Total and External. Char- 
acteristic Curves of a Series 
Dynamo. 



276 ELECTRICIANS' HANDY BOOK. 

Interpretation of Characteristic Curves.— The resistance of a 
working dynamo and its circuit is made up of various compo- 
nents. The total characteristic gives the equivalent in ohmic 
resistance of true and spurious resistance under different condi- 
tions. By Ohm's law resistance is equal to electromotive force 

divided by current, "or R = ^ 

In the characteristic curve diagram, E is given by the vertical 
distance (ordinate), I by the horizontal distance (abscissa). 
Dividing one by the other, we get resistance in ohms. Or draw- 
ing a line from the lower left-hand corner (origin) to any point 
on the curve, the tangent of the angle that line makes with the 
horizontal line will be proportional to the resistance at the point 
in question. 

This gives another basis for interpretation. If resistance is 
increased, the line making with the horizontal an angle whose 
tangent is equal to the resistance will swing back to the left, so 
as to increase the angle. This increasing of the angle will 
increase the tangent, which is as it should be, because the tangent 
represents resistance, which by the conditions assumed also in- 
creases. Such a line is called sometimes the vector line of watts. 

As it approaches the vertical the tangent increases, and if the 
value of the current intensity, or of I, is kept constant, the value 
of the electromotive force or of E will increase. When the 
tangent of the angle becomes infinitely great, then an infinite 
electromotive force will be required to maintain a finite current. 

Data for External Characteristic Curves.— When the volt- 
meter and ammeter have been used to determine the relations of 
current and electromotive force in a dynamo under different out- 
puts, the data are obtained for characteristic curves. Here an 
important distinction is to be drawn. The voltmeter gives the 
potential difference existing on the outer circuit only. The 
amperes given by the ammeter are those which pass through the 
whole circuit. 

Data for Total Characteristic Curves. — This is a distinction 
which often has to be made. Amperes are identical over all parts 
of a circuit. Volts vary in proportion to the relative resistances 
of the parts of the circuit affected. If, having obtained the data 



CHARACTERISTIC CURVES. 277 

for an external characteristic, the electromotive force of the 
whole circuit can be substituted for the potential difference given 
by the voltmeter, the new data will give the total characteristic. 
The resistance of the dynamo being known. Ohm's law gives 
the electromotive force of the system. Suppose a current of 50 
amperes is taken on the external characteristic, the dotted line 
curve e, Fig. 171; this gives 60 volts. By Ohm's law the external 

resistance is equal to _or — = 1-2 ohms. The internal resist- 
I 00 

ance of the particular dynamo tested was 0.6 ohm. The total 

resistance of the circuit was therefore 1.2 + 0.6 = 1.8 ohms. The 

electromotive force of the whole circuit at 50 amperes of current 

is now deduced by Ohm's law: B = R I ==: 1.8 X 50 = 90 volts. 

Drawing Characteristic Curves. — In the ways above described 
a number of points on a characteristic curve are found, and from 
these the curve is constructed. For each value of current strength 
a value of voltage as given by the voltmeter for an external 
characteristic is given, and a value of electromotive force calcu- 
lated as above for the total characteristic is also given. 

These points are marked upon a sheet of paper. The current 
rneasurements are taken on horizontal lines, the voltage and 
electromotive force measurements on vertical lines. The curve 
is then drawn through these points. A thin flexible strip of wood 
called a spline is a simple appliance for such purposes. A more 
efficient instrument is the flexible ruler. Its construction is 
based on the use of a bar of lead. This is bent to any desired 
curve, and holds its shape. The splines spring back when re- 
leased. 

The easier characteristic to get is the external. It has to 
precede the total characteristic. Its data are absolute and useful. 
The data of the total calculated as described leave armature 
reactians out of account. When a characteristic is given and no 
statement is made that it is a total characteristic, it may be 
taken as an external one. It is bad practice not to state whether 
a characteristic is external or total. 

Internal Characteristic— It is obvious that there is an inter- 
nal characteristic. This is based on unvarying resistance. It is 
therefore a straight line. 



278 



ELECTRICIANS' HANDY BOOK. 



We may prove this by returning to the radius vector of watts. 
If resistance is constant, the tangents of all radius vectors of 
watts must be constant. This is equivalent to saying that all 
such radius vectors must coincide in direction. They will all ho 
represented therefore by parts of one straight line. They will 

vary among themselves 
Y only in length measured 

from the lower left-hand 
corner (origin). 

Terminology of Ana- 
lytical Geometry . —The 
word given in parenthe- 
ses is one of the terms 
used in analytical geom- 
etry. The vertical line 
on the left is the axis 
of Y or of ordinates; the 
lower horizontal line is 
the axis of X or of abscis- 
sas; horizontal lines are 
abscissas; vertical lines 
are ordinates; the inter- 
section of the axes of X 
and Y is the origin. 

Line of Ohms.— The 
diagram hitherto has not 
directly shown ohms. It 
is divided into squares. 
A diagonal to the lower 
left-hand square drawn from the origin will be an angle of 45" 
with the horizontal, and its tangent will be 1. This is taken as 1 
ohm. The vertical line or ordinate through the right-hand end of 
this square is taken as the line of ohms. A radius vector of watts 
drawn to any part of the curve will have its tangent given by the 
part of this vertical line cut off. The value of this tangent will 
give the ohms resistance. In the diagram, Fig. 172, the resist- 
ance at the point B is 2 ohms, at A 4 ohms, and so on. 

The line of ohms is erected on the point 10 of the base line. 



100 
90 










-M 




- 


E""" 


1 


^ 




f 






80 


C_„.. 


4 


/ 


/ 


/; 






60 
t]50 
40 
30 
20 
10 


CO 

S 


I 




/ 


1 






UJ 

— § 


' 


/ 




1 






1 \ 


/ 




1 






1 


/ 






i 

i 








/\ 






1 






1/ 


i 












V 


1 






!f 







10 



.20 



30 40 

AMPERES 



50 60 



70 



Fig. 



172.— Line of Ohms in Character- 
istic Curve Diagram. 



CHARACTERISTIC CURVES. 279 

The line from O to B is the radius vector of watts. It intersects 

the line of ohms at a distance 2 from the base, taking the side of 

a square as unity. This shows that at the point B the resistance 

is 2 ohms. As B corresponds to 90 volts and 45 amperes, by 

E 90 volts „ , , . , 

Ohm's law R = — • = or 2 ohms, which corresponds 

-L 45 amperes 

with the diagram. 

On the same diagram the resistance line, or line of ohms, can 
be used for either internal or external characteristic. The inter- 
section of the internal radius vector of watts with it will give 
the constant internal resistance. 

General Notes on Characteristic Curves. — The changes of 
resistance are effected by the manipulation of the outer circuit 
by the observer. Resistance is thrown in and out as desired, in 
order to get the different points of the characteristic. 

To give a characteristic any meaning, one of the factors must 
be kept constant. This is always the revolutions per minute. 
But a characteristic could be based on fixed resistance, and the 
changes in current and voltage could be brought about by varying 
the speed. Then the tangents of the radius vectors of the watts 
curve being equal as denoting the resistance, the curve would 
merge into a straight line. 

Fixed current might be the basis. Then the characteristic 
would become a simple vertical line. Its position would give the 
amperage. Its length would give the voltage as long as the 
resistance was unchanged. If the resistance was increased, the 
radius vector would cut it higher up, and the voltage v/ould be 
given by the place of intersection. 

Fixed voltage as a basis would give a horizontal line, whose 
length would give the amperage. The intersection of the radius 
vector with this line determines the amperage corresponding to 
any desired resistance. 

This makes it clear why characteristics are given with fixed 
speed of rotation. The straight lines do not give the peculiarities 
of a dynamo as fully as do the curves. By changing the speed, 
we virtually change one dynamo into another. 

Critical Current. — A characteristic curve of a series dynamo 
starts as a nearly straight line. At its beginning its radius 



280 ELECTRICIANS' HANDY BOOK. 

vectors are virtually one except in length. At first doubling the 
voltage doubles the current approximately. But after a while the 
curve bends to the right. On examining Fig. 170, it will be seen 
that for a given increase in voltage, the amperage will increase 
more rapidly than before. The point where this change is 
noticeable is a sort of critical point. The current corresponding 
to it is called the critical current. It is obvious that there is 
nothing accurate about it. The critical current is the minimum 
current required to excite the field. With insufficient ampere 
turns, a field magnet will not produce an adequate intensity of 
field. Therefore with a series dynamo too high an external 
resistance, cutting down the current, will weaken the field. This 
weakening may be enough to arrest the dynamo in its functions, 
and cause it to give hardly any electromotive force. It may 
easily prevent it starting into action from inaction. 

A series dynamo must be started on low external resistance, 
and the resistance must never be so high as to cut the current 
down below the critical value. 

The electromotive force given by a dynamo increases with the 
speed. The resistance may accordingly be increased as the speed 
increases without affecting the current. Therefore there is no 
critical speed or critical resistance for a series dynamo, except 
in the most general sense on short circuit. 

Shunt=Wound Dynamo Characteristics. — There are three pos- 
sible characteristics of this type of machine. One is the total 
characteristic, which includes the armature current and the 
electromotive force. The armature current is equal to the sum 
of the currents passing through the field winding and shunt 
winding. The second is the external characteristic. This is 
based on the voltage between terminals and the total current of 
the outer circuit. This current is a part only of the armature 
current. The third is the so-called internal characteristic. This 
is based on the same voltage as for the second case and on the 
amperes in the shunt or field magnet windings. Possibly some 
ingenious person might evolve a fourth and a fifth characteristic, 
taking the armature into cases two and three. In practice the 
external and internal characteristics are most used. These are 
the second and third of the preceding list. 



CHARACTERISTIC CURVES. 



281 



Critical Point of Shunt=Wound D^^namo. — The external char- 
acteristic of a shunt-wound dynamo is given in Fig. 173. It 
begins at the top at P. On open circuit all the current is shunted 
into the field, and the voltage between terminals reaches its max- 
imum. The resistance of the outer circuit when open is infinite. 
The outer circuit is now closed 
through a- very high resistance. 
This shunts a certain amount 
of current from the field coil, 
and weakens the field so as to 
reduce the voltage. The resist- 
ance is gradually lowered, 
shunting more and more cur- 
rent from the field as more 
passes through the external cir- 
cuit, until a sort of critical 
point is reached. This point is 
where a reduction of external 
resistance begins to rob the 
field of so much current that 
the electromotive force falls 
more rapidly than before. At 
this point the watts are at a 
maximum. At last the curve, 
at the 35-volt-32-ampere point 
in Fig. 173, reaches a point of 
instability, and with very little 
change of resistance runs down 
to a zero value. 

The horse-power curves are 
interesting in their relations to the characteristic. The ordi- 
nate or vertical next to the left-hand axis of ordinates can be 
used as an ohm line. A straight edge will then give the resistance 
for each point on the curve. At P it is infinite, because the tan- 
gent of an angle of 90° is infinite. The volts at P were obtained on 
open circuit, which is infinite in resistance. 

In the case shown in Fig. 173 the critical current may be 
called 32 amperes. It is not critical to the same extent as in a 



^ 


\ 


\ 

\ 
\ 






\ 

\ 
V 










^ 








\ 
\ 


/ 






\ / 


N 
■s 




y 






y 









10 20 30 ' 10 

AMPERES 

Fig. 173.— Externai. CharactHristig 
OF A Shunt-Wotini> Dynamo 

WITH HORSE-POWEB LiNES. 



282 



ELECTRICIANS' HANDY BOOK. 



series dynamo. But the long, almost straight descent of the 
curve toward the origin gives a critical factor. This is external 
resistance. With insufficient external resistance the electromo- 
tive force falls to zero. With infinite resistance it rises to a 
maximum. At an intermediate resistance, which in this particu- 
lar case is about one ohm, the power is ready to rise rapidly or 
fall rapidly for a slight change in resistance. If the outer resist- 
ance is increased, the power rises on account of an increase in 




Fig. 174.— Outer Circuit and Total 
Current Characteristic in 
A Shunt Dynamo. 




Fig. 175.— Total Charactbbistio 
or &nuNT Dynamo. 



voltage. If the resistance decreases, the power falls by an 
almost equal decrease of voltage and current. 

Roughly speaking, the characteristic shows one horse-power 
with a resistance of 1 ohm and a resistance of 6 ohms. With 
a resistance of about 1% ohms it shows the maximum power, 
nearly 2 horse-power. These variations in resistance are in the 
external circuit. 

Total Current Characteristic in Shunt Dynamo. — The total 
current is that which flows through the armature, and which is 
the sum of currents in the field coil and in the external circuit. 
The characteristic of the external circuit as just deduced is the 



CHARACTERISTIC CURVES. 



283 



basis. The new one is drawn by adding to the abscissas or to the 
horizontal lines of the diagram, lengths representing the current 
which at each given voltage will flow through the field. 

In the cut, Fig. 174, the inner of the two curves is the charac- 
teristic of the outer circuit. The radius vector is drawn at an 
angle giving a tangent equal to the armature resistance. A 
straight line is the characteristic when the resistance is con- 
stant. Therefore, the distance e s is the amperes of current 
which would exist in the armature at the voltage corresponding 
thereto. This and the corresponding lengths are then added each 
to the corresponding abscissa of the external curve, as at m n 




70 




60 


^ 


50 


- /^ 


^40 


- 1 SHUNT MACHINE 


>30 


/ 


20 


- / 


10 


] 



4 5 

OHMS 



Figs. 176 AND 177.— Ohm- YoLT Curve of Series and Shunt Dynamos. 



and i i^ and the new curve is drawn through the points thus 
determined. The outer curve is the total current characteristic 
thus constructed. 

Total Characteristic of Sliunt Dynamo.— So far the curves 
have been based on potential difference at the terminals. To 
get the characteristic based on total electromotive force and 
total current, we start with the curve of total current e. Fig. 
175. The radius vector J gives the armature characteristic. Take 
a point p. Fig. 175, on the curve of total current. This is on an 
ordinate denoting p e amperes. The voltage of the armature at 
this current is the length a x. This added to p x, the voltage at 
the terminals, gives the electromotive force q x 2X the amperage 
O X. In this way points are found on a curve which give the 



284 



ELECTRICIANS' HANDY BOOK. 




relations between the electromotive force and total current, just 
as described for other cases. 
Ohm- Volt Curves. — Curves can be laid out with the resistance 

of the circuit as one of the ele- 

YlB . ___H D ments. In parallel lighting 

service the resistance of the 
outer circuit increases as 
lamps are extinguished, and 
decreases as they are lighted. 
The ohm-volt curve is espe- 
cially adapted for expressing 
the conditions of such service. 
Two such curves are shown on 
a small scale in Figs. 176 
and 177, one for a series dy- 
namo, one for a shunt dyna- 
mo. For a compound dyna- 
mo the corresponding curve 
is a combination of the two. 
In Fig. 178 the curves are su- 
perimposed. It will be seen that if combined, the result will be 
a straight voltage line. This is the condition desired for parallel 
circuit lighting and supply, where the voltage should be constant 
under all changes of resistance. 

Thus the sum of B G and B F is ^qual to H E. This line repre- 
sents the sum of the voltages of the curves at the resistance de- 
noted by B. The same summation at other points would give 
other points representing the sum of the voltages of the two 
curves at various resistances. The locus of these points, or the 
place where they would be found, would be a line approximately 
straight and horizontal; it is the line B D of the cut. The line 
B D is the combination of the other two curves and indicates their 
combined action. This action is that of giving identical voltage 
at varying resistances. 



OHMS 



Pig. 178.— Combined Series and Shunt 
Ohm- Volt Curves for a Compound- 
Wound Machine. 



CHAPTER XVI. 

THE DIRECT-CURRENT MOTOR. 

Direct=Current Electric Motor and Torque. — The direct-cur- 
rent electric motor is a machine driven by the direct current 
which is generated in any desired way, which current is forced 
through it by electromotive force. As motors are constructed in 
modern engineering practice, the driving of the motor causes the 
armature to rotate. This it does with greater or less force, and the 
force developed is torque. Torque is a twisting or turning force. 

The armature driven around with torque or twisting force is 
connected to machines, so as to do useful work. 

Reversibility of Dynamo and Motor. — It is only a few years 
ago that the doctrine of the conservation of energy was definitely 
formulated and accepted as the cornerstone of natural science. 
In nothing is it better illustrated than in the reversibility of the 
dynamo and motor. If such a machine is turned by mechanical 
power, resistance will be encountered if the circuit is closed, and 
mechanical energy will be absorbed. On the circuit, by the heat- 
ing of the wire and other means, the presence of electrical energy 
can be discerned. Energy is conserved. The mechanical energy 
expended in driving the machine has not disappeared; it has 
been converted into electrical energy. 

In the motor exactly the opposite action takes place. Electri- 
cal energy is absorbed by the motor, and mechanical energy 
is given off by it. It is another example of the conservation of 
energy. The same machine can act in one or the other role. In 
engineering practice an electric machine often automatically 
changes from motor to dynamo, or the reverse. Sometimes this 
action is a cause of serious trouble if not detected in time. 

Generator and Motor Connected.. — If we have two direct- 
current machines connected by two leads, so as to form a com- 



286 



ELECTRICIANS' HANDY BOOK. 



plete circuit, and both are turning, each one in turning will gener- 
ate electromotive force. Referring now to the cut, Fig. 179, there 
are shown two such machines connected, and both armatures are 
supposed to rotate in the direction indicated by the upper arrow. 
The polarity of the electromotive force due to rotation tends 
upward from the lower brush to the upper. This tendency is 
indicated by the arrows on the end of the armature pointing 
upward. 

The condition of things shown in the cut is the operation of a 
generator and motor on one circuit; both are direct-current and 



GENERATOR 




LINE 



RETURN 




Fig, 179.— Connection of Generator and Motor. 



L 



bipolar. The bipolar type is selected for the sake of simplicity. 
What is to be noted applies to all direct-current machines. 

Counter Electromotive Force. — The left-hand machine is the 
generator sending current over the line and throu^ the coils 
of its armature. The latter begins to revolve. As it does so, it 
generates in accordance with Lenz's law electromotive force, 
which operates to resist its rotation. This it does by opposing 
the electromotive force on the line, thereby cutting down the 
driving current. Such an opposing electromotive force is called 
counter electromotive force, and is indicated by the arrows on 
the end of the armature. 

This example illustrates a broad principle underlying the 
operation of direct-current machines primarily. If in a direct- 



THE DIRECT-CURRENT MOTOR. 287 

current machine the electromotive force and current are in 
harmony with each other, working in the same direction, the 
machine is a generator. If the current forced through the ma- 
chine and the electromotive force due to its rotation oppose each 
other, the machine is a motor. 

The above applies to alternating-current synchronous motors 
operated by single-phase current, as will be seen later. 

Action of Counter Electromotive Force. — Counter electromo- 
tive force tends to reduce the speed of rotation of direct-current 
motors. It does this without any direct waste of power. A 
motor may work with highest efficiency at a certain rate of speed. 
If the counter electromotive force reduced it below this speed, its 
efficiency would be reduced, but there would be no direct relation 
necessarily between the counter electromotive force and the reduc- 
tion in efficiency. Counter electromotive force is not a hurtful 
resistance. 

Counter electromotive force tends to prevent a direct-current 
motor from going too fast. The faster its armature rotates, the 
greater will be the counter electromotive force produced, and the 
less will be the torque of the machine. The torque will diminish, 
because the current will diminish as the counter electromotive 
force increases. As the armature turns against mechanical re- 
sistance of various kinds, friction, air resistance, and sometimes 
a load such as that due to machinery driven by it, the reduction 
of torque reduces the speed of rotation. 

Relation of Speeds of Generator and flotor Connected.— If 
the two machines are identical, and if the motor turned without 
any friction or resistance of any kind, the greatest speed the 
motor could attain would be equal to that of the generator. 
Identical armatures rotating at identical speed in identical fields 
of force generate the same electromotive force. In the generator 
and motor these would be opposed to each other; and when the 
motor turned at the same speed as the generator, no current 
would pass. In the condition supposed, the armatures would 
rotate synchronously, and no mechanical energy would be gener- 
ated in the generator or expended in the motor. Such syn- 
chronism could not possibly exist, as no armature could rotate 
without experiencing some resistance. 



288 ELECTRICIANS' HANDY BOOK. 

The slower a motor runs, other things being equal, the greater 
will be the current passing through it, and the greater will be 
the net electromotive force producing the current. The voll- 
amperes will be greater therefore as a motor runs more slowly, 
and slow running is due to increased mechanical resistance. The 
volt-amperes represent energy absorbed; the mechanical resist- 
ance overcome represents energy developed. As is manifestly 
proper, they increase and diminish together. 

Counter Electromotive Force and the Armature. — The arma- 
ture of a working motor is ordinarily of such low resistance that 
the current which would pass through it at the potential of the 
working circuit would heat it so much as to injure it. As the 
armature rotates it has counter electromotive force impressed upon 
it, which acts like resistance, and reduces the current passing 
through it. Counter electromotive force protects the armature 
from burning out. Reduction of current in the armature re- 
duces torque, so that the turning force of the armature is re- 
duced as its speed of rotation increases. Thus a slowly-turning 
armature takes more current and exerts higher torque than a 
rapidly-rotating one. To protect it from burning out a rheostat 
is generally used to start it, so that it begins rotating with a re- 
duced current, only receiving the full electromotive force of the 
circuit when it is turning fast enough to protect itself by counter 
electromotive force. 



1 



L 



CHAPTER XVII. 

OPEN-COIL. AND HOMOPOLAR GENERATORS— SIZE AND 
OUTPUT OF GENERATORS. 

Opea=Coil Armature Winding. — The windings of tlie armature 
of a direct-current dynamo need not be re-entrant. In the one- 
coil armature they are disconnected at the ends, as is seen in 
Figs. 133 and 126, page 220. The old two-pole magnetos and dy- 
namos with single-coil armature of the H type, Fig. 128, page 223, 
all operated on this principle. The G-ramme ring, introducing into 
the larger field of engineering practice the older Pacinotti prin- 
ciple of clo&ed-coil winding, was hai'.ed as an immense advance. 
Yet to the present day the open-coil winding is used on some of the 
most successful dynamos. 

The Brush Dynamo uses open-circuit windings. The diagram. 
Fig. 180, shows the principle of the armature winding. The 
coils are carried on an iron ring-shaped core, which is a variety 
of the Gramme-ring core. The coils may be of any even number; 
for each pair of coils opposite to each other there is what amounts 
to one two-part commutator. 

Returning to the diagram. Fig. 180, the outer end of each 
armature coil is connected to a commutator bar or segment, as 
indicated in plane development. The inner ends of each pair of 
opposite coils are connected across the armature to each other. 

When a pair of coils are in the neighborhood of the vertical 
line, or in the position of coils Ci Ca, the maximum number of 
lines of force are passing through them. For the instant the 
path of these lines of force coincides with the path followed by 
the coil, so that there is no change in the number passing through 
the coil for that instant. Hence the coil is inactive and is out of 
circuit, no brush contacts being made with its commutator seg- 
ments. 

From the coils Aj A2, which on account of armature reaction 



290 



ELECTRICIANS' HANDY BOOK. 



are in the position of best action, current is talven by the brushes 
P Q. The arrows give the direction of the current. From 
brush Q the current goes to brush R. The coils Bi Bj have left 
the position of best action, and hence have less electromotive 
force impressed upon them than have the coils Ai As. The same 
applies to the coils Dj Do as regards electromotive force, for 
converse reason, that these coils Di D, are approaching but have 
not reached the position of best action. The brush Q, taking the 




dSE 




Fig. 180.— Development op the Brush Dynamo Winding. 



current from A., delivers it to the B and D coils, four in number, 
in parallel of two, by the brush R. It divides between them, re- 
unites at brush S, goes through the field P M, and outer circuit 
back to P. 

The object of dividing the current between coils Bi B, and 
Di D2 in parallel is in a sort of accordance with Ohm's law. The 
electromotive force in these coils being below the maximum, the 
resistance is also reduced by connecting them in parallel. 



OPEN-COIL AXD HOMOPOLAR GENERATORS. 



291 



Each pair of coils in a Brush machine can be pictured as rep- 
resenting an open-coil independent armature of two coils. Thus 
an eight-coil machine is in a sense equivalent to four independent 
machines, caused to co-operate in producing a pulsating direct 
current. 

Brush Dynamo Construction. — In Fig. 180a is shown a Brush 
dynamo with its upper field section removed and its armature 
hoisted up out of its bearings. It shows the ring armature with 
grouped windings, On the shaft are rings of larger diameter 




. . Fig. 180a.— Brush Dynamo. 

than that of the shaft which carries them. These are oiling rings. 
When the armature is in place, these hang with their lower sec- 
tion immersed in oil. As the shaft rotates they turn also, travel- 
ing around it and carrying up oil to it so as to continuously feed 
the bearings with oil. This is termed ring oiling. 

The Thomson= Houston Armature is wound on the open-circuit 
principle. The armature contains a group of three coils, or three 
sets of coils and a three-part commutator. The coils are wound 
on a hollow spheroidal frame, and the resulting armature is 
nearly spherical in shape. The coils are all wound in the same 
sense, right or left-handed. Three ends of the coil windings 
a're connected together; the other three ends go to three commu- 



292 



ELECTRICIANS' HANDY BOOK. 



tator divisions. In the newer machines a ring armature has 
been used. 

The diagram. Fig, 181, shows the connections. Three ends of 
the coils are connected together at D, as shown; three go to the 
commutator segments. A, B, and C. The small arrows show the 
direction of the current. 

The coils consist of numerous turns of wire; the diagram shows 
each as a single turn for the sake of simplicity. 

The next diagram, Fig. 182, shows the coils as three radii, 
A, B, and C, connecting three commutator segments. Each 

radius represents a great num- 
ber of turns of conductor on the 
core. F P are four brushes ; L L 
indicate lamps on the outer cir- 
cuit. Arrows show the direction 
of the current, and a curved ar- 
row shows the direction of rota- 
tion of the armature. The dotted 
lines mn show the position of 
the neutral line of the field. 

Coil B in the diagram is in the 
neutral position, and is cut out. 
The positions of coils A, B, and 
C may be referred to the figures 
on a clock face. B is at 10 
o'clock, A is at 2 o'clock, and C is at 6 o'clock. In this po- 
sition current goes from C to A. When the armature turns 
so as to bring B a little further on, it connects with the 
brush F', and this coil B through the brush F" and the coil 
C through the brush P' work in parallel with each other and 
in series with A. Next C moves on toward 4 o'clock, and is cut 
out, leaving A and B working in series with each other. As A 
passes on toward 10 o'clock, just before it parts company with 
the brush P, the brush F comes in contact with C, and A and C 
are in parallel with each other and in series with B. 

In practice the angular distance between the brush ends P' 
and F' and the brush ends P and F is about 60° respectively, and 
this keeps the parallel pair of coils in parallel with each other 
for some considerable part of the rotation. 




Fig. 181.— Thomson-Houston 
Armature Winding. 



OPEN-COIL AND HOMOPOLAR GENERATORS. 



293 



The dynamo is automatically regulated by moving the brushes 
P F' backward or away from P P', and shifting P P' forward 
when more current is needed and vice versa. If the angular dis- 
tance between the brush ends P and F and the brush ends P' and 
F' is 60°, there will be no period when all the section coils are 
not doing something, two being always in parallel with each other. 
By bringing the brushes closer together the current is dimin- 
ished by increasing the period of time during which one of the 
coils is cut out and inactive. 

Homopolar, Acyclic or Unipolar Dynamo. — We have seen 
that a closed ring swept through a uniform field of force has no 
current induced in it, although electromotive force is impressed 
on it. Electromotive force is impressed upon its two halves of 




Fig. 183.— Diagram of Cibctjtts of Thomson-Houston Dtnamo. 

the same polarity in each, so that they counteract each other. If to 
opposite ends of the horizontal diameter of the ring, as shown in 
the drawing, Fig. 115, the ends of a conductor were connected, 
current would go through it. A simple conductor representing 
the vertical diameter of the circle could take its place, and nat- 
urally would. A current is thus produced by sweeping a con- 
ductor through a uniform field of force, and without varying the 
number of lines of force which are interlinked with the circuit. 
A generator constructed on this basis is named as above. 

Up to the present time, comparatively few have been made. 

Various ways of producing the field can be used. Let cylin- 
drical north and south poles of a dynamo face each other. The 
axis of the armature corresponding with the center of the cylin- 



294 ELECTRICIANS' HANDY BOOK. 

drical field, radial conductors swept through it will have elec- 
tromotive force impressed upon them, and if one brush connects 
with the inner and one with the outer end of a radial con- 
ductor, current can be taken from the brushes. The conductors 
cannot be connected as in ordinary dynamos, but the brushes 
must take current from opposite ends of the conductor. Any 
number can be put in the armature, and are connected to col- 
lecting rings, so as to carry out the principle described. 

Two north poles may be placed within two south poles, thus 
making an annular or ring-shaped field. A conductor swept 
through this field, and lying parallel with the axis of the field, 
will have electromotive force impressed upon it, and a current 
can be taken from brushes connecting with its ends. Any num- 
ber of conductors can be placed in the field, so as to form a 
hollow cylinder. They cannot be connected, as in a drum arma- 
ture, or one will counteract the other. The current has to be 
taken from their ends. 

Owing to the absence of a commutator, this type of machine 
presents great advantages as a generator of direct current. Its 
names are derived from the feature that the active conductors 
move through a field of uniform or unvarying density. 

Relation of Size and Output of Dynamos. — Considerable dis- 
cussion has been given to the question of the relation of the 
sizes of identically-shaped electric current generators to their 
respective outputs. If a dynamo is reproduced in all its relative 
proportions, but of double the linear dimensions, what will be 
the relative power output of the two? 

Manufacturer's and Thompson's Rules — One rough rule is to 
treat the output as varying with the weight. This is a manu- 
facturer's rule, a mere approximation to accuracy. It is express- 
ed in mathematical terms by saying that the capacities of iden- 
tically proportioned dynamos vary with the cube of the linear 
dimensions. Prof. Silvanus P. Thompson has given the fifth 
power of the linear dimensions as the correct figure. 

If one dynamo was twice as large in linear dimensions as an- 
other, it would, according to the "manufacturer's rule," have 
eight times the capacity of the smaller one; according to Prof. 
Thompson's rule, it would have thirty-two times the capacity. 



OPEN-COIL AND HOMOPOLAR GENERATORS. 295 

This is a considerable discrepancy. Yet if we investigate it on 
a purely proportional basis, the discrepancy may be still greater. 

Deduction of Thompson's Factor.— Assume a dynamo of double 
the linear dimensions. The length of the magnetic circuit will 
be doubled. For identical value of magnetization or g twice the 
ampere turns will be needed. The wire on the field will have 
twice the diameter on the large dynamo of that of the wire on 
the small one. This will give it the same number of turns, but 
four times the capacity for current. Therefore the intensity of 
field or B will be multiplied by four on account of the increased 
current, and divided by two on account of the greater length of 
magnetic circuit, giving half the permeance per unit of cross 
section. This is a net increase of field intensity to twice that 
existing in the smaller dynamo. 

The field will have four times the cross-sectional area. There- 
fore being of twice the intensity, the lines of force in it will 
be 4 X 2 = 8, or eight times as many as in the smaller dynamo. 

The armature will have twice the linear dimensions of the 
smaller one, and therefore can carry twice the turns of wire 
per layer and twice as many layers as the smaller one carried. 
'This gives four times as many convolutions. If it rotates at the 
same number of revolutions per minute as does the smaller 
armature, it will cut 8X4=: 32, or thirty-two times as many lines 
of force as did the armature one-half its size in linear dimen- 
sions. This gives thirty-two times the voltage. This coefllcient 
32 is the fifth power of 2, or 2^ = 32. If we stopped here, we 
should have Prof. S. P. Thompson's figure. The output of a 
dynamo is governed by the voltage it can produce, and by the 
amperage it can carry. The size of the armature wire con- 
trols the amperage. It must not be subjected to so heavy a cur- 
rent as to get overheated. If it is assumed to be of the same 
size in the larger as in the smaller dynamo, the larger one will 
give the same current at thirty-two times the voltage, which 
gives thirty-two times the capacity in watts. 

The rule of the fifth power thus deduced is not rigorously ac- 
curate, because sources of loss vary with the sizes of dynamos, 
and tend to favor the output of the larger sizes. 

In the above calculation a doubling of intensity of field mag- 



296 ELECTRICIANS' HANDY BOOK. 

netization is assumed. This is not to be looked for in praK,-tice. 
With equal excitation, the output would be reduced to 16, or 2^ 
times that of the smaller. 

The Sixth=Power Rule.— If we assume the air gap to be in- 
creased in depth or thickness, and the same field intensity to 
be maintained, we can get a still higher result. 

Assume the field of equal intensity to be of four times the 
area. Assume that the same voltage is to be impressed on the 
circuit. Then one-fourth the windings are required on the arma- 
ture, as there are four times as many lines of force in the field. 
To put one-fourth the windings on an armature of twice the 
circumference, the wire should have eight times the diameter of 
the wire on the smaller armature. But a wire of eight times 
the diameter of another one can carry 8^ = 64, or sixty-four times 
the current, giving an output sixty-four times as great as that of 
the generator which is half its size in linear dimensions. 

Both of these deductions are on the basis of an equal number 
of revolutions of the armature per minute. It would be nearer 
truth to take an identical peripheral velocity. 

This would reduce 2^ or 32 to 2* or 16, and 2^ or 64 to 2^ or 32. 
The latter figure allows for an increase of the thickness of the* 
air and copper gap in the larger machine to eight times what it 
was in the smaller one. This is certainly excessive. 

Calling n the relative linear size of the larger dynamo, the 
authorities give the student his choice of the following powers 
of n to express the increased output of the n times larger dy- 
namo: 

Prescott n^ 

Mascart and Joubert n^ 

Hopkinson n^ 

Rechniewski n^ 

Manufacturer's Rule, a little over n^ 

Ayrton n^*'^ 

Frolich w* 

Deprez n^ 

Thompson, S. P n^ 

All things considered, the fourth power or n* is a safe figure 
to take. 



CHAPTER XVIII. 

GENERATOR AND MOTOR CONSTRUCTION. 

Disks for Smooth=Surface Armature Cores.— To prevent the 
production of eddy currents of serious intensity, armature cores 
are built up of thin sheets or disks of iron. Disks are cut to 
give the cross section of the drum, and are laid up with sheets 






Figs. 183 to 186.— Smooth-Con tour Core Disks. 

of paper intervening to form a cylindrical pile. The disks are 
often cut with a large hole in the center. They are often fastened 
together with bolts, which run through the pile of iron and 
paper from end to end. The bolts are insulated by tubes of in- 
sulating material. The cylindrical core thus produced may be 

297 



298 



ELECTRICIANS' HANDY BOOK. 



keyed directly to the main shaft, or is carried by spiders. The 
cuts. Figs. 183 to 188, show various examples of core disks with 





Figs. 187 and 188.- Smooth-Contoub Core Disks with Spiders. 



smooth contour. Sometimes the core is built up of segments 
of disks, as shown in Pig. 189. 

Disks for Grooved Armature Cores.— A general practice in 
drum armatures is to have a series of longitudinal grooves in 
the cylindrical core surface to receive the conductors. Disks for 
these are cut out with peripheral notches, as shown in Figs. 190 
to 192. 



Fig. 




Segmentai. Core Disk Construction. 



However carefully the piling up of such disks is done, the 
notches or grooves are not to be relied on as being perfectly 
true and smooth. Smoothness is essential to avoid cutting the 
insulation. Accordingly, each core thus built up is often placed 
in a filing machine, where the long grooves are filed out one by 
one until they are of exact size and smooth. This constitutes the 
armature core, which is keyed to the armature shaft of the 
machine. In Fig. 193 is shown such a core. 



GENERATOR AND MOTOR CONSTRUCTION. 



299 



Formed Colls.— The material of the winding differs for differ- 
ent machines. It may be composed of round wire, of square wire, 
or of flat bars. In some works each coil is shaped on a form to 




Figs/ 190 to 193.— Disks for GtROOved Armatube Cores. 

the exact contour of the place where it is to lie on the armature. 
In the case of a heavy bar of copper, this exacts some rather elab- 
orate bending. Sometimes an iron jig is used for this purpose, 
sometimes it is done largely by hand process. In any case, each 




— Laminat:^d DituM Armature Core on Shaft. 



coil or element appears as an irregular rectangle. Such coils ar<5 
termed formed coils. American practice favors the use of formed 
coils, whenever it is possible to employ them. They are shown 
in Figs. 194 to 196. 

Wire Winding.— The older way of winding armatures was the 
simple process of hand-winding with insulated wire. This is 



30Q 



ELECTRICIANS' HANDY BOOK. 




Figs. 19 1 to 196.-Formed Coils for Armatures. 

Still used to a considerable extent, but formed coils for dynamos 
and other electric apparatus are typical of modern methods. 

Insulation of Conductors.— Alcoholic solution of shellac is 
much employed in insulating armature conductors. Formed 



GENERATOR AND MOTOR CONSTRUCTION. 



301 



conductors are taped, shellacked, and baked before being set into 
the grooves on the armature core. 

Core Grooves and Wooden Wedges. — Little notches are some- 
times formed in the notches in the core disks. When the core 
is built up, these give a dovetailed groove next to the periphery 
or surface of the core. Long slips of wood are driven into these 
grooves and above the windings, holding the latter firn:\ly in 




Figs. 197 and 198,— Winding Armatures with Formed Coils. 



place. Wire bindings are wound around the whole in three or 
more places for additional security. 

Winding Armatures with Formed Coils.— The cuts, Figs. 197 
and 198, illustrate the insertion of formed coils in the grooves in 
armature cores, and the next cuts, Figs. 199, 200, and 201, show 
armatures completely wound. 

Pole Armatures.— This type of construction is not very much 
used, except for alternating currents. The cut, Fig. 202, shows 
a sectional view of a multipolar pole armature in a multipolar- 
field. As tbe armature rotates, its winrlin°"s are cnrn'pd through 
high intensities of field, whpu role facp« nole as in the cut. 
In the position when armature poles would face the space be- 



302 



ELECTRICIANS' HANDY BOOK. 




Figs. 199, 200 and 201.— Armatttres C0MPt.BTT5T.T Wound. 

tween field poles, the field would be weak. Thus, in rotating the 
armature coils would be interlinked with constantly-varying 
numbers of lines of force, so that currents would be induced in 
them. The construction shown is that used for the Ganz-Ziper- 
nowski alternator, but will serve to show the principle of the polar 



GENERATOR AND MOTOR CONSTRUCTION. 



303 



type of armature. Fig. 202a shows a multipolar structure wliich 
may be an armature or a revolving field. 

Disk Armature. — This is also a type of armature which is but 
little used. Fig. 203 shows a field magnet producing a field 
of force of straight lines. The spaces on one or the other side 
of the poles have an exceedingly weak field. To show the 
action of the poles, a wire conductor is shown, which moved 
in the direction of the large arrows would have electromotive 
force impressed upon it of the polarity indicated by the small 




Fig. 203.— Pole Armature. 



arrows in Figs. 203 and 203a. The last-named cut shows the com- 
plete set of coils of the armature, part only of which is shown in 
Fig. 203. 

The next cut. Fig. 204, shows the section of the active field 
of a disk dynamo, through which such coils as those shown in 
diagram in Fig. 205 are swept. 

Commutator Construction. — The commutator is huilt up of 
a number of bars of nearly rectangular section. They are made 
of hard-drawn copper. They are put together like the staves of a 
barrel, the periphery being made up of their edges, not of their 
flat sides. It is as if the staves of a barrel were but an inch 
in width and several inches deep or thick. The commutator bars 
have placed between them strips of insulating material, made 
partly or entirely of mica. 



304 



ELECTRICIANS' HANDY BOOK. 



Mica is an excellent insulator; it is mechanically strong, can 
be bent to a considerable extent, and is absolutely non-combustible 
and unaffected by any heat it can ever be subjected to on a dyna- 
mo or in electrical machinery. No substitute for it has ever been 
found. It is made up into various preparations, resembling card- 
board, and these are put 
upon the market by var- 
ious manufacturers. 

A hollow cylinder with 
thick walls is built up of 
the copper bars and insu- 
lating strips, and the 
pieces have to be firmly 
secured without any elec- 
trical contact between 
them. They must be rig- 
idly held in position, be- 
cause the commutator 
has to be turned up be- 
tween centers, and any 
motion of the bars would 
be fatal to securing a 
cylindrical surface. The 
surface has to be cylin- 
drical, or the brushes will 
jump and chatter. A high 
bar or one out of position 
will interfere with the ac- 
tion of the machine. The bars must be secure from displacement. 
The cuts, Figs. 206 to 209, show various constructions of com- 
mutator. The heavy dark lines indicate insulation. The views 
are given in section, and are self-explanatory. 

The function of the commutator is usually to transfer the 
rubbing contact from outside periphery to a drum of relatively 
small diameter. In some machines the commutator is of almost 
the full diameter of the armature. In any case it provides a 
smooth cylindrical surface for the brushes to rest upon. In the 
drum and ring armatures the brushes could take the current from 




Fig. 203a.— MTTLTTPOT.An Akmatttre ob 
Revolving Field. 



GENERATOR AND MOTOR CONSTRUCTION. 



305 



the conductors on the periphery of the drum or ring as the case 
may be, were it not for mechanical considerations. 
Position of Commutators. — The commutator is keyed on the 




Figs. 203 and 303a.— Disk Armature Induction. 

armature shaft. It must be accurately in center with it, and 
its surface must conform to the requirements stated. The end 
disks o*r spiders which hold it to the shaft are seen in the cuts, 
and the insulation between them and the commutator bars is 



^ 



m. 



-z^- 



^ 



Fig. 20t.--SECTiON of FiEiiD and 
Armature of Disk Dynamo. 




Fig. 305.— Armature Coils op Disk 
Dynamo. 



shown in the cuts. In Figs. 199, 200, and 201, page 302, are shown 
different arrangements of commutators and armature. 
Brushes and Brush Holders, — The name brush is applied 



306 



ELECTRICIAN8' HANDY BOOK. 



to the conductor, generally very unlike a brush, which bears 
against a moving surface, also a conductor, so as to make an 
electric contact. The moving part may be a simple insulated 
ring upon a rotating shaft, it may even be a shaft, or is a com- 
mutator with conducting segments insulated from the shaft and 
from each other. 




Fig. 306.— Section of Commutator and Bruph Mou: ting. 

In direct-current dynamos such as are being now described, the 
brushes bear against the cylindrical surface of the commutator. 

Tangential Brushes. — The first brushes were springs of metal 
placed tangentially, and pressing against the ring or commuta- 
tor. These were succeeded by compound brushes made of a 
number of pieces of copper secured one on top of the other and 



GENERATOR AND MOTOR CONSTRUCTION. 



307 



beveled and trimmed accurately square at the end, so as to line 
with the commutator divisions. Wire gauze is a constituent of 
some brushes, and carbon bearing directly or radially on the 





C 

Tig. 207.— Commutator Construction. 




Fig. 208.— Section of Commutator and Brush Mounting. 



surface of the commutator is now the generally accepted type of 
brush. It presents advantages not possessed by other brushes. 

Trimming Metal Brushes.— Metal brushes must fit the com- 
mutator circle with their hollow beveled ends, and must be 



308 



ELECTRICIANS' HANDY BOOK. 



trimmed perfectly square. Gauges are provided for the pur- 
pose. A sharp cold chisel may be used, or a shears may suffice. 
A little touching up with a file may be needed. If a file is used, 
no filings must be left on the metal, as they might stick between 
the commutator segments and short-circuit the bars. 

Radial Brushes. — The 
construction of a radial car- 
bon brush and brush holder 
is shown in the cut, Fig. 210. 
A block of carbon is held in 
a socket. The block must 
move freely in the socket 




FiQo 209.— Section of Commutator 
AND Brush Mounting. 



Fig. 210.— Radial Brush and 
Holder. 



and must be free from side shake. It is pushed downward 
by a flat spring, and rests upon the commutator surface. The 
lower surface of the carbon is shaped to fit the commutator. 
The spring is so long that its pressure is sensibly even for dif- 
ferent lengths of carbon blocks. The carbon blocks constantly 
wear, so this feature of even pressure, whether they are long or 
short, which is equivalent to old or new, is a valuable one. 

Another brush mounting is shown in Fig. 211. Here the brush 
is fastened in a socket by a clamping screw, and a spiral pres- 
sure spring forces the brush against the commutator. The 
block is held by strips of hard copper, which act like springs 
and conduct the current. 



GENERATOR AND MOTOR CONSTRUCTION. 



309 



An important advantage in radial brushes is that if an arma- 
ture accidentally in starting or stopping, or while out of action, 
should be turned backward, radial brushes will be uninjured, 
while tangential or inclined ones will probably get caught in the 
commutator and be bent back and injured, so that they will re- 
quire straightening and trimming before the dynamo can be 
started again. 

Position of Opposite Brushes.— Brushes on opposite sides 
should not be set so as to bear upon exactly the same zone of 



/ir\ CLAMPING SCREW 




Fig. 211. -Radial Bbtjsh and Holder, 



the commutator. They should be staggered a little, so as to bear 
upon the whole surface of the commutator as near as may be. 

Brush Rigging. — In multipolar machines, the brushes are some- 
times carried in sets on two insulated rings, which are carried 
on a metallic ring. For the latter a seat is turned in the frame 
of the machine. In Fig. 212 is illustrated the "brush rigging" as 
it is called of an eight-pole machine, and the next cut shows a 
set of the brushes. The mounting of a brush of one of these 
sets is shown in Fig. 211. The two rings are called the posi- 
tive and negative bus rings. 

A commutator is always apt to wear a little uneven. The brush 
holders are made as light as possible, so as to follow any irregu- 



310 



ELECTRICIANS' HANDY BOOK. 



larities of shape of the commutator. A properly-treated commu- 
tator with brushes of good quality will wear very evenly. 

Relation of Depth of Air Gap to Sparking. — To avoid spark- 
ing, equal induction should be exerted by each pole. This is in- 
sured by equal permeance of the magnetic circuit. An unequal 

depth of air gap is the most 
potent disturbing cause. Some 
irregularity often results from 
wearing of the bearings, which 
throws the armature out of 




Fig. 313.— Brush Rigging fob a 
Multipolar Dynamo. 



Fig. 313. 



-Brushes of Same Brush 
Rigging. 



center, and diminishes the air gaps on one side and increases 
them on the other. To minimize the trouble resulting from this 
displacement, it is a standard practice to make the air gap rather 
deep. A small displacement of the armature shaft under these 
circumstances has less disturbing effect than it would with very 
small air gaps. A reduction of a thirty-second of an inch would 
not be of much effect in a half-inch air gap, while the same re- 
duction would reduce a one-sixteenth-inch air gap fifty per cent, 
and bring about very irregular or one-sided induction. 

Field riagnet for Multipolar Dynamos.— Almost all large dy- 
namos are now made of the multipolar type. The poles are often 
short cylinders carried on the inner surface of a heavy polygonal 



1^ 



GENERATOR AND MOTOR CONSTRUCTION. 



311 



or circular iron frame as shown in Figs. 214, 215, and 216. The 
poles project radially toward the center. The frame constitutes 
the field yoke. It is often made in two parts joined on the hori- 
zontal diameter, and the poles lie on the diagonals of the circle as 
shown. The effect of this is that the upper half of the field can 




Fig. 214.— Four-Pole Dynamo Frame 

WITH Section op Winding 

ON One Pole. 



Fig. 315.— MuLTiPOiiAB Dynamo 

Frame Showing Brackets eor 

Carrying Brush Rigging. 



he lifted off without touching the armature surface, a very essen- 
tial requirement, as any rubbing of pole face against the surface 
of the windings might Injure the insulation. 

In some machines the pole pieces are made of steel and cast- 
welded into the frame. This process is executed by imbedding the 
pole pieces in the mold, letting their ends project into the space 
where the metal for the semi-circles of the field frame is to run. 
The melted cast iron makes a perfect joint with the steel. 

Cast-iron pole pieces are used upon some of the machines. 

Formed coils are often used on poles as shown in Fig. 217. 
Sometimes they are wound with flat conductors bent edgewise as 
shown in Fig, 217a. 

To illustrate what has preceded, the cut, Fig. 218, may be re- 



312 



ELECTRICIANS' HANDY BOOK. 



ferred to. It shows the principal parts of a four-pole dynamo, the 
rear post, which carries the armature bearing, being omitted to 
avoid confusion. The ring system of oil feeding is used, and 




Fig. 216.— pole and Pole "Winding of 
MuLTiPOi/AB Dynamo. 



Pig. 217.— Pole Winding 
WITH Formed Coils. 




Fig. 217a.— Edgewise Bent Field Winding and Pole 



ring oilers are shown under the left end of the edgewise armature 
shaft. The loose rings Avhen in place rest upon the revolving 
shaft bearing and turn with it, picking up oil and feeding it to the 
shaft. 



GENERATOR AND MOTOR CONSTRUCTION. ZU 




314 



ELECTRICIANS' HANDY BOOK. 



Laminated Field Magnets. — Sometimes the field is made up of 
laminations cut as shown in Figs. 219, 220, and 221. The windings 
lie in the inner notches, and are so placed as to establish alter- 
nate poles all around the circle. The plates are insulated with 



paper. 
Sectional 



Laminated Field flagnets.— The laminated field j 








&^:.mm^^m5oyi^ 




Figs. 319, 220 and 231.— Laminated T'iei.ds. 

magnets on large dynamos are often made in sections, as shown 
in Figs. 222 and 223. These pieces are bolted together so as to 
form a circle. It will be noticed that the lower one has perfor- 
ations, and not notches. The windings are passed through these 
holes, and a very solid construction is the result. 



GENERATOR AND MOTOR CONSTRUCTION. 315 

Such fields as those shown in Figs. 219 to 223 are most used 
in alternating-current generators. 

Details of Multipolar Field Windings.— The windings of the 
field poles are often made on tin spools with deep flanges, the 
surface being most thoroughly insulated by mica, paper, and 
cloth. One by one these are wound full of wire, which is shel- 




FiQS. 222 AND 223.— Sectional, Laminations for Field Magnets. 

lacked and baked, so as to produce a solid mass, ready to be 
slipped upon the pole. 

A laminated pole piece placed over the end of each cylindrical 
pole holds the winding in place. It projects on both sides of it, 
and is hollowed out accurately to the circle of the armature. The 
space between it and the armature constitutes the air gap. 

The field castings have to be carefully machined before being 
set up. The bases and joint faces are planed off, the sections are 
bolted together, and the inner faces of the poles are then turned 
off. 



CHAPTER XIX. 

THE ALTERNATING CURRENT. 

Alternating Electromotive Force.— Although the term alter- 
nating current is universally used, alternating electromotive 
force is its producer, and precedes it often. The true original is 
generally alternating electromotive force. 

An alternating electromotive force is one which alternates in 
polarity, regularly or in obedience to some law. It starts at a 
value of zero, rises to a maximum of one polarity, descends to a 
value of zero again, changing in direction reaches a maximum of 
opposite polarity, whence it returns to zero again. Thes€ alterna- 
tions are repeated over and over again. 

Cycle, Wave, and Frequency. — The changes described in the 
last sentence constitute a cycle or wave of alternating electro- 
motive force. If for the word "polarity" we substitute the word 
"direction," the sentence will describe a cycle or wave of alternat- 
ing current. When a wave of alternating current or of alternating 
electromotive force reaches its point of greatest value, the whole 
circuit is affected; when it reaches zero value, the whole circuit 
is at zero. The expression wave must be clearly understood. It 
does not mean that waves run over the circuit, but it does mean 
that the whole circuit passes simultaneously through the values 
of the cycle, ranging from zero to a maximum in one direction, 
back through zero to a maximum in the other direction, and 
then back to zero, completing a wave. The number of waves per 
second is called the frequency of the alternating electromotive 
force or current. 

Electromotive Force rnd Current Curve. — We often gain in 
our conceptions of things by analogies. It is evident that the 
action of such electromotive force is analogous to that of a wave. 
A line representing the cross section of a wave would be a con- 

316 



THE ALTERNATING CURRENT. 



317 



venient way of picturing to the mind the action of alternating 
electromotive force. It is so good a representation that it is 
i^niversally used. 

Such a line is shown in the cut, Fig. 224. 

The horizontal line is what the geometrician would call the 
locus (place) of zero values. The vertical lines are drawn of 
length corresponding to the distance of points of the curve from 
the horizontal or base line. They are called ordinates of the 
curve. The curve comprises one full wave or cycle. 

The portions of the curve below the horizontal line represent 
the electromotive force of one polarity; the portions above the 
line that of the other polarity. The lengths of the ordinates rep- 
resent the strengths of the electromotive force. The shape of 




270' 
Fig. 324.— Sine Curve of Generating Circle. 



the curve represents the way the electromotive force increases 
and diminishes. 

If the proper conditions prevailed, an alternating current of 
exactly identical form would be produced by the alternating 
electromotive force. A similar curve would represent the cur- 
rent, its ordinates would indicate by their length the intensities 
of the current. Their position above or below the zero line would 
indicate the direction of the current constantly changing; for 
part of the cycle in one direction and for part of the cycle in the 
reverse direction. 

The current is the factor generally referred to in practice; 
alternating electromotive force is its invariable cause and con- 
comitant. An alternating-current generator is also an alternat- 
ing electromotive force generator, and an alternating-current sys- 



318 ELECTRICIANS' HANDY BOOK. 

tern is an alternating electromotive force system. It is thus 
through all the branches of alternating-current work. But the 
expression "alternating current" is always used, except where 
there is special reason for using the other expression, "alternat- 
ing electromotive force." 

Production of Alternating Electromotive Force and Current. 
— Alternating electromotive force is impressed upon a circuit by 
means of a special type of electric machine called an alternating 
current dynamo, alternating current generator, or alternator. In 
practice the armature contains one, two, or three separate wind- 
ings. The terminals of the windings are connected to various 
numbers of leads constituting the outer circuit. The armature 
is so wound that its entire winding is simultaneously impressed 
with the same electromotive force at the same instant, but this 
electromotive force varies though the values of the wave or cycle 
just described. In turning through the arc represented by the 
quotient of 360° divided by half tl^e number of poles in the field 
of the alternator, one cycle or wave of alternating electromotive 
force is impressed upon each of the armature windings and cir- 
cuit. 

The above is strictly true for typical alternators, but is sub- 
ject to modification for some constructions. 

Length of a Wave. — A wave curve is divided into or measured 
by 360 parts. This refers its length directly to degree measure- 
ment, as there are 360 degrees in a circle. Such system har- 
monizes with the fact that alternating electromotive force is 
always generated by the circular motion of an armature or field, 
and that a single wave is produced by a complete rotation of the 
armature or field through 360 degrees, or by a rotation through 
an integral portion of 360 degrees. 

Form of Alternating E. M. F. and Current.— The form of 
the curve represents the nature of the variations of the electro- 
motive force or current, as the case may be. The form of a cur- 
rent is the nature of its variations, and is graphically represented 
by its curve. The same applies to electromotive force. An al- 
ternating current may increase slowly or suddenly, by an even 
curve or a series of jumps, and may return to zero value in var- 
ious ways also. If it is to be represented loj a curve, the irregu- 



^N. 



THE ALTERNATING CURRENT. 



319 



larities of the current will be shown in its form. Hence the form 
of the current is spoken of, and expresses the consecutive varia- 
I tions in intensity. In Figs. 225 and 226 waves of various forms 
are shown. The dotted lines represent in each case separate 
waves of exactly the same length. The two dotted lines com- 
bined produce as a resultant in each case the heavy black line, 
which gives a third wave form. 

Length of Wave and Frequency. — Waves of the same fre- 
quency are those which are produced the same number of times 
in a given period of time. The curves representing them are 




// 


^\ 






p 


\ 






// 


A 






1/ 


\ 






,/--., 


,.----, \ 


-' — ■ . 




f"" 


-\ 






/ 


\ 




V 


1 -•' 


\\' 






7 


^ 


*-r^ 


J 




^ 


^^r^ 


>^ 



Figs. 225 and 226.— Waves of Different Forms and 

RESUIiTANT OF TwO WAVES. 



drawn of the same length per wave if the waves are of the same 
frequency. In the diagrams of waves in this section of this book, 
the waves on each diagram are of the same frequency, and are 
therefore drawn of the same length. 

Cause of the Form of Alternating Electromotive Force and 
Current. — The waves of current may vary in form, and the form 
depends upon the construction of the generator, with particular 
reference to the shape of the field-magnet pole pieces and of the 
armature core. The distribution of lines of force through the 
field may be varied indefinitely by changing the shape of the 
poles, even if the armature core is left unaltered. The current 
varies in intensity as the rate of change of the number of lines of 
force interlinked with the circuit varies. This rate of change de- 



320 



ELECTRICIANS' RANDY BOOK. 



pends on the distribution of lines of force in the field. Hence 
any form, within reasonable limits, can be given to the alternat- 
ing electromotive force and current waves. The form universally 
striven after is known as the sine curve. 

Alternating Electromotive Force and Current Curves. — When 
an alternating electromotive force is producing a current, separ- 
ate curves may be drawn for each. One zero or base line is used 
for both curves. The portions of the electromotive force curve 
above the line represent the portions of the electromotive force 
producing current represented by the portions of the current 




Fig. 227.— Current and Electromotive Force Curves. 

curve above the line. The same applies to the curves below the 
line. The length of a wave of current must be rigorously equal 
to that of a wave of electromotive force producing it. The height 
may be different, and as a matter of convenience usually is so 
drawn. Fig. 227 shows two such wave curves. The current curve 
may cross the zero line at the same points where the electromotive 
force current does, or may not, according to the conditions of the 
circuit. The single zero line or base line is the locus or place 
where current and electromotive force have zero value. When 
the current curve crosses this line, it indicates that the current 
at that instant ceases to exist. It is the point when it reverses 



ib 



THE ALTERNATING CURRENT. 321 

its direction, dropping to zero in one direction and starting in 
the other direction from zero. The same applies to alternating 
electromotive force and its polarity. 
Drawing the Electromotive Force and Current Curves.— A 

straight horizontal line is drawn, and a portion of it is taken to 
represent the period of time taken by the system to produce one 
wave or cycle. For several reasons it is most convenient to divide 
this into periods of time, each equal to 1/360 of the period of a 
cycle or some integral divisor of 360, such 1/36 or 1/16. Suppose 
the line is divided into sixteen parts; at each a perpendicular is 
drawn. These are called ordinates of the curve. If electromotive 
force is the subject, each ordinate is drawn of length proportional 
to the voltage at the period it represents. For one polarity the 
ordinates are laid off upward, for the other polarity downward. 
Through their ends a line is drawn, and this represents the form 
of the cycle. The same method can be used for alternating-cur- 
rent curves, the lines being drawn of length proportional to the 
amperage of the current at different periods of the cycle. The 
method is illustrated in Fig. 224. 

Degree System. — The portion of the zero line containing or 
subtending a complete wave, consisting of one positive and one 
negative portion, is by the degree system divided into the 360 di- 
visions as described, each division representing one angular degree 
of rotation of a two-pole armature in a two-pole magnetic field. 
This armature may be only hypothetical. If the armature is four- 
pole and rotates in a four-pole field, each degree on the zero 
line of the current curve or electromotive force curve will repre- 
sent one-half of a degree of its rotation; if it is a six-pole con- 
struction, one-third of a degree will be represented, and so on. 
Thus the ordinate at any point by the degree system can be re- 
ferred to some point in the rotation of the rotor of the alter- 
nator. This indicates a reason for referring the divisions of the 
zero line to degree measurement. The form of the alternating 
current almost universally used in represented by the sine curve, 
and to make the construction of the curve intelligible and easy, 
the degree system is essential. 

The Sine Curve. — The sine curve or curve of sines, as it is 
also called, is shown in Fig. 224, and is based on the following 



322 ELECTRICIANS' HANDY BOOK. 

principles: On a horizontal base line are erected perpendiculars. 
The line is divided into 360 parts, representing degrees of a circle. 
Each perpendicular is laid off equal in length to the sine of the 
angle expressed by the degree mark on which it stands. Up to 
the 180th division the perpendiculars are on one side of the base 
line; for the rest of the 360 divisions they are below it. The 
curve can also be drawn by the use of what is called the gener- 
ating circle. 

Generating Circle.— At one end of the horizontal zero line a 
circle, as in Fig. 224, is drawn, with its center on the line. Sines 
of various angles are drawn, and from the end of each sine a 
horizontal line is drawn, under or over the zero line, according 
to the position of the sines. The intersection of each horizontal 
line with a perpendicular to the base line erected on it at a point 
corresponding to the degrees of the arc of the sine gives a point 
on the sine curve. The arcs begin at the right-hand end of the 
horizontal diameter of the circle. Half of the sines are above 
and half below the base line, and the complete circumference 
of the circle gives the sines to determine the ordinates for one 
full cycle or wave. In the cut 22%° is the angle used in the 
construction. 

The curve is drawn through the ends of the lines. The com- 
plete circumference of the circle gives one full wave. 

An ellipse or various other figures or closed curves could be 
substituted for the circle, when other forms of waves would be 
produc-ed. In practice the circle only is used, as the tendency 
of engineering is in the direction of the production of sine curve 
currents. 

By reference to the generating circle, the sine curve may be 
thus simply described. Imagine the periphery of a circle straight- 
ened out so as to become a straight line. Mark upon it the de- 
grees of the circle. Erect perpendiculars on each degree mark, 
for the first 180° above the line, for the rest below it, and make 
each line equal in length to the sine of the angle indicated by 
its degree mark. The curve is drawn through the ends of these 
lines. 

The construction is shown in the cut, Fig. 224. The left-hand 
quadrant of the generating circle is divided into angles of 22^^°, 



THE ALTERNATING CURRENT. ^.23 

or one-sixteenth of a circumference. For each angle sines are 
drawn, such as M P. On the base line divisions corresponding to 
the angles are laid off, and ordinates erected on them. Bach sine 
determines the length of the ordinate corresponding to its angle. 
Thus, the sine MP of 45° determines the length of the ordinate 
M P erected on the second or 45° of the sixteen divisions of the 
horizontal base line. 

Interpretation of the Generating Circle. — It is not necessary 
to draw a sine curve to represent the form of this universal type 
of alternating-current cycle. The cycle can be represented by the 
circle alone. Thus, the line drawn from the horizontal diameter, 
perpendicular to it, and intersecting the circle at any point, gives 
the value of the electromotive force or current at the instant 
represented by that point on the circle. This line at 90° has a 
maximum value. This means that when a period is one-quarter 
advanced from its beginning, the electromotive force or the cur- 
rent, as the case may be, has its maximum value. The same 
applies to the 270° of the circle. Values below the diameter are 
of polarity or direction opposite to that of values above it. At 
180° the value of the perpendicular is zero, and after that it be- 
gins to increase in the opposite direction. This means that when 
the cycle is one-half completed, the electromotive force or cur- 
rent, as the case may be, has a value of zero, and immediately 
begins to increase, but in the opposite polarity or direction. 

Rate of Change. — At the top or bottom of the loops the curve 
for two consecutive points is horizontal, where for an infinitely 
small period it moves parallel to the base line. Hence, if it rep- 
resents current strength, the current for this instant will not 
change. Where the curve crosses the base line there is a place 
where the curve between two consecutive points is most steeply 
inclined to the horizontal line. At this place it approaches the 
vertical direction nearer than elsewhere, and at this place the 
electromotive force or current, whichever the curve represents, 
is changing most rapidly in value. It has here its highest rate 
of change. 

Graphic Representation of Rate of Change.— If a radius 
sweeps through the arc of a quadrant, the successive sines will 
indicate the successive values of the alternating curi'ent it may 



324 



ELECTRICIANS' HANDY BOOK. 



be taken as representing. As it starts from 0°, the sines will in- 
crease most rapidly in length and their rate of change will be 
greatest. As it approaches 90°, the sines will increase least rap- 
idly in length for a given angular change, or their rate of change 
will be least. Let a second radius at 90° from the first be as- 
sumed to move around with the first one, always remaining per- 
pendicular to it. The sines of the angles fixed by the positions 
of this second radius give the rate of change of current or elec- 
tromotive force corresponding to the sine curve of the other or 
first radius. In Fig. 228 the two radii are shown, one marked 

R. of Ch. being the radius 
vector of rate of change. 

As a sine curve can be 
drawn from the first radius, 
a second one can be drawn 
from the other; the second 
sine curve will be a rate-of- 
change curve. The rate of 
change at any given point of 
the first curve will be pro- 
portional to the ordinate of 
the second curve at this 
point. The two curves will 
occupy fixed positions with 
reference to each other. 
They are said to be in quad- 
rature with each other, as 
will be explained later. Fig. 
232 may be referred to as showing two curves generated by radius 
vectors at right angles to each other. 

Radius Vector and Resultant.— A line may be drawn from 
a common center or point called the origin, and may have two 
qualities. One is its length. This may be greater or less; and 
as the line is to be taken as representing a quantity, the length 
of the line must be proportional to the quantity it represents. 
This proportional size is determined by reference to some other 
line, otherwise the question of length would not come into con- 
sideration. The other quality is its angular position with refer- 




FiG. 238.— Radius Vector or Rate of 
Change. 



THE ALTERNATING CURRENT. 



325 




Fig. 239.- Vectors and Resultant. 



ence to any other quantity, which quantity is taken as indicated 

by another line drawn from the origin as before. The angular 

position is the number 
of degrees included be- 
tween the two lines. 

Thus, suppose two 
quantities represented 
by two lines, Fig. 229, 
OB and O C, drawn 
from a common center 

at an angle with each other and one longer than the other. They 

would indicate two quantities out of phase with each other and 

one greater than the other. They would form two sides of a 

parallelogram, whose diagonal O N from the origin O outward 

would be their resultant, and would represent the combined effect 

of both quantities. 
Vector Diagram of a 

Sine Curve.— From the 

center of a generating 

circle as shown in Fig. 

230, radius vectors are 

drawn at equal angular 

distances around the cir- 
cle. Each radius has 

marked upon it a point 

equal in distance from 

the center to the length 

of the sine of its angle. 

In the diagram, O Q is 

laid off on OP equal in 

length to the sine of 60°. 

The same is done for the 

other radius vectors, and a curve is drawn. For one-half of the 

wave this is a circle of half the diameter of the generating circle. 

Two circles one above and one below the zero line represent the 

full wave of a sine curve. 
Phase, Lag, and Lead. — The length of a wave of impressed 

electromotive force is exactly equal to that of the wave of cur- 




FiG 330.— Vector Dtagkam of Sine 
Curve. 



326 



ELECTRICIANS' HANDY BOOK. 



rent it produces. The waves also correspond in form, although 
in order to secure clearness in diagrams one set are often diawn 
of lower height than that of the other set. The two sets of 
waves may be in identical positions. This means that as each 
wave of electromotive force is impressed on the circuit, a cor- 
responding wave of current accompanies it. At the instant when 
the electromotive force is greatest, the current would be greatest. 
Such waves are said to be in phase with each other, and are 
shown in Fig. 231. 

In this and the following wave diagrams, the figures 1, 2, ... . 
with the vertical lines enable the relations of the curves to be 
seen. 

If the waves of alternating electromotive force take a certain 




Of T z: 

Fig. 231.— Waves in Phase. 



Fig. 232.— Waves in Quadrature. 



time to produce the current waves, so that the current wave 
reaches its highest intensity after the electromotive force wave 
producing it has begun to diminish, the current waves are said 
to lag. 

Such a condition is shown in diagram in Fig. 232 by the one 
set of waves lagging behind the other, crossing the zero line 
later than the others. 

The reverse may hold. One set of waves may reach their 
height before the other set reaches it. They are said to lead, 
which condition Fig. 232 also serves to illustrate. Such condi- 
tion is shown in diagram by the one set of waves reaching their 
highest points while the other set are still rising. 

Angle of Lead and Lag. — We have seen that angular measure- 
ment can be applied to waves, and that the length of a wave is 



THE ALTERNATING CURRENT. 



327 



360°. A fraction of the length of a wave is expressed in de- 
grees. Half a wave is 180°, one-quarter of a wave is 90°, and 
so on. The difference in period between two waves is expressed 
therefore in degrees also. One set may lag 40° behind the other; 
as 40° is 1/9 of 360°, a lag of 40° means a lag of 1/9 of a Wave 
length. The same applies to all lags and leads. The expression 
in degrees is called the angle of lag or of lead as the case may 
be. It is designated by B. 

Quadrature and Opposition.— If the angle of lag or of lead be- 
tween two sets of waves is 90°, which is the quarter of a circle, 
the waves are said to be in quadrature with each other. The 
waves of Fig. 232 are in quadrature. 

If the angle of lag or of lead is 180°, the waves are said to be 
in opposition, as shown in Fig. 
233. 

Basis of Lag and Lead.— 
The waves of alternating elec- 
tromotive force are the usual 
basis — the current waves are 
said to lag or lead. But if the 
current leads the electromotive 
force lags, and sometimes the 
current is employed as basis. 
A diagram of sine curves of 

two sets of waves, out of phase with each other, can be interpreted 
in two ways — as showing one set lagging or the other set leading. 

Average Values. — The average intensity of a sine current is 
equal to the average of the sines. As half are positive and half 
are negative in value, the average value of the current is zero. 
This is more simply put if the current is simply thought of as 
alternating, half one way and half the other, and therefore as 
neutralizing itself. 

This is begging the question. The thing that concerns the 
electrician is the practical value of the alternating current. It 
is a component of energy under proper conditions both coming 
and going. 

The average value of the ordinates of a sine wave gives the 
average value of the thing it represents. It can be expressed 




Fig. 233.— Waves in Opposition. 



328 ELECTRICIANS' HANDY BOOK. 

as a fraction of the longest of the vertical lines. By geometrical 
process it is proved to be equal to 0.63633 of the maximum ordi- 
nate, the longest of the vertical lines — it is nearly two-thirds of 
the line indicating the height of the crest. This figure is of little 
practical use, because what the engineer is concerned with is the 
power on his circuit. In the case of direct current, the product 
of electromotive force by amperes gives the power. Direct-cur- 
rent power plants operate either at constant potential or con- 
stant current, while the electromotive force and current are con- 
stantly varying in alternating-current distribution. The formulas 

for energy rate or power I E, P R, and Jz. are given in a preceding 

R 

section of this book. The two latter can be used for alternating 

current work, to get two of the factors for the power of the 

circuit — the effective electromotive force and effective current. 

Effective Values. — The square of the value of a current is pro- 
portional to the watts it can produce in a conductor of definite 
resistance. The watt or volt-ampere is expressed by E I and by 
PR and the latter expression shows that with a fixed resistance 
the watts produced by a current vary with the square of the 
current. 

The effective value of an alternating current is expressed as 
the intensity of a direct current which would with the same re- 
sistance develop the same number of watts. This current would 
produce the same quantity of heat with the same resistance. 
Doubling the current with the same resistance would give four 
times the heat. 

The heating effect of an alternating current at any instant is 
proportional to the square of its intensity at that instant. The 
average of the squares of the values of the current through a 
half cycle is proportional to the average heating effect of the 
current. The square root of this average value is the effective 
value of the current. 

Calculation of Effective Values.— Taking PR and ^ as ex- 

R 

pressions for the rate of energy in a circuit, if the average value 

of the squares of current or of electromotive force be taken, it 
will give the expressions for average power. If the square 



THE ALTERNATING CURRENT. 329 

root of average P or average E- be extracted, it will give wliat 
is known as the effective values of current and electromotive 
force. The effective value of an alternating quantity is defined 
as the square root of the mean square of the ordinates of the 
sine curve. The effective value is thus calculated. 

Both the sines and cosines of the respective arcs of a quad- 
rant vary exactly in the same ratio, but oppositely or comple- 
mentarily disposed on all parts of a quadrant. We have the re- 
lation sin^Q + cos^ = 1, if the radius is equal to unity. As the 
sine and cosine vary in the identical ratio, the average sine- is 
equal to the average cosine-. Therefore from these considera- 
tions we have: 

Average sin- + average cos- 0=1 

Average sin- = average cos' disregarding the signs and 
only concerning ourselves with the numerical value. 

.*. 2 X average sin^ G = 1 

Average sin- 6 = % . 

Average sin =^/~T/ = 0.7071. 

N A- 1.41 + 

This gives us the factor used in obtaining the effective value 
of the thing shown by the sine curve. The effective value is then 
equal to the maximum value multiplied by 0.7071. The maximum 
value in the unitary circle is 1, and the formula is therefore ap- 
plicable to other cases by substituting for 1 the value of the liin 
9(5° X radius =: radius. 

Form Factor, — The quotient obtained by dividing the effective 
value by the mean value varies with the form of the curve. For a 

sine curve the value is =1.11. This value is called the form 

- ^ (iat) 
factor. 

This factor is of interest as giving the relative heating powers 
of alternating and direct currents. The alternating current will 
have about eleven per cent more heating power than will the 
direct current, which is of the same average strength. 

If an alternating current voltmeter is placed upon a circuit 
in which the volts range from +100 to — 100, it will read 70.7 
volts, although the arithmetical average, irrespective of + or — 
sign, is really 63.7 volts. If a direct electromotive force were 



330 ELECTRICIANS' HANDY BOOK. 

to act upon the same instrument, it would have to be of 70.7 volts 
value, to give the same reading. 

If an alternating sine current ammeter reads 100 amperes, it 
means that the current fluctuates from +141.4 to — 141.4 am- 
peres, but produces the same heating effect as if it were a 100- 
ampere direct current. 

An interesting point to be made here is that if a generator 
is wound with two windings for alternating currents, its effective 
electromotive force will be 1.11 times higher than if operated 
as a direct-current dynamo, by commutator and proper connec- 
tions. If wound with one open circuit of wire with two end con- 
nections to the collecting rings, its electromotive force will be 2.22 
times higher. 

The tendency of an electromotive force on a circuit to cause 
the piercing of the insulation depends on the maximum voltage. 
This voltage must be taken cognizance of for this and similar 
effects. 

If on a Siemens dynamometer the current given by an alternator 
was found to be any given number of amperes, the maximum cur- 
rent would be found by dividing the reading by 0.707, or by multi- 
plying by 1.41+. 

Formulas for Effective Values. — The values can be expressed 
as vulgar fractions thus: 

I max 
Effective current =r == ' * 

E max 

Effective electromotive force = ^^3^ 

It will be noticed that in cases where the electromotive force or 
current intensity has been determined by an apparatus, it is 
always the effective values that are given by the readings of the 
instrument. As these are the working values, the coefficient 0.707 
is of comparatively little use in practical working. 

Power Factor. — The rate of energy or the power developed in &. 
circuit by a direct current is expressed by E I. This will not 
answer for the alternating sine current. The periodic change 
in its values renders a constant necessary, with which the prod- 
uct of the effective current intensity by the effective electro- 



THE ALTERNATING CURRENT: 331 

motive force is multiplied to give the average power. This is a 

practical quantity; it is the cosine of the angle of lag, or cos q). 

^ E max J max 
Average E I or power = cos cp. 

Call effective current I, and effective electromotive force E. 

The equations for the effective values of current and electromotive 

force on page 330 give us the values of B max and I max, thus: 

E max 
E=: =:r or Emax = E. y'2 

v^ 

I m:x 

1= — ^or I max = I. a/ 2 

Substituting for E max and I max in the first equation their 
' values as above, we have: 

Average E I or power =: EI cos q). 
In this equation B and I are the effective values, such as would 
be determined by a voltmeter and ammeter adapted for alternat- 
ing currents. 

The factor cos' q) is called the power factor. 
Suppose the angle of lag is 90°, or that electromotive force and 
current are in quadrature with each other. In this case^= 90° 
and cos 90° = 0. Therefore, the power factor being zero, the 
power when the current and electromotive force are in quadrature 
with each other is of zero value. This is the case of a wattless 
current. 

A cosine has its greatest value, which is unity, when its angle 
is G°. Therefore when<7>=0 the power is at its greatest, and is 
equal to the product of the effective values of electromotive force 
and current intensity. This case is when there is no lag of cur- 
rent, or when the current and electromotive force are in phase. 

Qualities of a Circuit. — There are three qualities of a circuit 
which affect the action of alternating current and electromotive 
force upon it — resistance, inductance, and capacity. Each one 
has two effects — one effect upon the current, the other effect 
upon the phase relations of electromotive force and current. 

Resistance acts to reduce alternating current, just as it does 
in the case of a direct current, in accordance with Ohm's law. 
This action upon an alternating current is greatest when the 



332 ELECTRICIANS' HANDY BOOK. 

current is greatest, as at the top of the wave, and is without 
effect when the current is zero, represented by the sine curve cross- 
ing the zero line; in other words, it has most effect when it has 
most material to work upon. Its second action is to tend to bring 
alternating current and alternating electromotive force into phase 
with each other. 

Reactance.. — The rate of alternating current which can pass 
through a circuit is modified by the resistance, inductance, and 
capacity in the circuit. The effects of each on the current can be 
indicated by ohms; the retarding effect of inductance and the 
reverse effect of capacity can be expressed in ohms, just as if they 
were resistance. 

The ohmic values of capacity and inductance are called react- 
ances — capacity reactance and induction reactance. 

If the reactances and resistance of a circuit are known, its effect 
upon an alternating current is determined by Ohm's law subjected 
to certain modifications. 

Inductance. — ^^The relation of lines of force to current is in- 
duction. Current produced in a circuit by changes in the lines 
of force interlinked in it is induced current, and electromotive 
force so produced is said to be impressed on the circuit. The rela- 
tions of lines of force produced by current in a circuit to that 
circuit constitute inductance or self-induction. As self-induc- 
tion is due to changes in current intensity, it is an all-important 
thing in alternating current practice, where the current varies 
in intensity many times in a second. 

Inductance in an alternating-current circuit acts to diminish 
or to absorb the electromotive force. It operates most when the 
current is at its zero value, because that is when the rate of 
change is greatest. This period is 90° removed from the period 
of maximum current, so that inductance acts in quadrature with 
resistance. Its second action is to cause the waves of current to 
lag behind those of the electromotive force. 

Inductance and the Henry.— Energy is required to create 
a field of force, but not to maintain it. Conductors are related 
in their properties to the field of force established about them 
by a current, or in other words vary in their property of estab- 
lishing fields of force under given current changes, which consti- - 



THE ALTERNATING CURRENT. 333 

tutes this property called self-induction or inductance, and which 
is measured by a unit called the henry. 

If a conductor is so constituted that a rate of change of cur- 
rent of one ampere per second in it requires the expenditure of 
one volt, it has an inductance of one henry. 

The same thing may be stated otherwise. If the inductance 
of a circuit is such that a current increasing one ampere per 
second produces in it a counter electromotive force of one volt, 
the circuit has an inductance of one henry. 

The henry is sometimes called the coefficient of inductance or 
of self-induction. 

It is generally indicated by the letter L. 

If the current in an active circuit decreases, the lines of force 
diminish and their potential energy becomes kinetic, and electro- 
motive force increasing, the normal current is induced on the 
circuit. 

Electromotive Force In an Alter nating= Current Circuit.— 
The electromotive force in an alternating-current circuit con- 
taining; inductance is partly expended in producing changes in 
the current. The electromotive force expended on increasing the 
current intensity varies with the rate of change. As the current 
increases, so also does the field density increase, and this in- 
crease of field density is what absorbs the energy indicated by 
the electromotive force multiplied by the current change. If 
the circumstances are such that the field diminishes in density, 
in so doing it generates electromotive force of the polarity cor- 
responding to that producing the current to which the lines of 
force are due. 

Cou*iter Electromotive Force.— This is the hypothetical elec- 
tromotive force opposed in polarity to the original impressed 
electromotive force, and due to inductance. It can only exist 
when the current is increasing in value. In an alternating-cur- 
rent circuit it appears when the current is increasing, and has 
the highest value when the current has the highest rate of change, 
which is when the current is passing from its period of zero 
value. It resists the action of impressed electromotive force, 
which produces an increasing current — that is to say, resists the 
current in the first and third quarters of a wave. 



334 ELECTRICIANS' HANDY BOOK. 

Forward Electromotive Force.— This is the hypothetical elec- 
tromotive force of the same polarity as the original, and is also 
due to inductance. It can only exist when the current is dimin- 
ishing in value, and has its highest value when the current is 
approaching zero value. It strengthens the action of impressed 
electromotive force which produces a diminishing current; it 
tends to increase the current in the second and fourth quarters of 
a wave when the impressed electromotive force would reduce it. 

Counter and Forward Electromotive Force in an Alternat= 
ing=Current Circuit.— From what has been said in the last two 
paragraphs, it will be seen that induced electromotive force in an 
alternating-current circuit, whether it be forward or counter 
electromotive force, opposes the action of the impressed electro- 
motive force. When the latter is rising in value, its action is 
opposed by counter electromotive force; when it is falling in 
value, its action is opposed by forward electromotive force. Hence 
inductance generates for an alternating current what is virtually 
counter electromotive force for all its phases. 

Turns of a Circuit and Inductance. — Assume a turn or con- 
volution of a wire constituting a part of an electric circuit. If an 
ampere of current is passed through it, it constitutes an ampere 
turn. Let a current starting from zero value, and increasing 
to a definite value in one second, be passed through it. The 
lines of force of the field called into being will exercise induc- 
tance and produce a certain amount of counter electromotive 
force, which may be called e. Assume that a second convolution 
of wire is added, so that the current has to go through two turns, 
instead of one. As this gives double the ampere turns, twice as 
many lines of force will be called into existence during the second 
of growth of a current equal in all respects to the one assumed. 
Each turn of wire will therefore be impressed with counter elec- 
tromotive force equal to 2e, because twice the lines of force of 
the first case act upon it. But there are two turns, each acted on 
by counter electromotive force of 2e. The total counter electro- 
motive force is therefore 4e. This gives the law: 

The inductance of a circuit is proportional to the square of the . 
number of its turns, if a constant rate of increase of current is 
maintained in it. 



THE ALTERNATING CURRENT. 335 

Reactance of Inductance.— A circuit opposes to the passage of 
an electric current, whether such current be constant or varying, 
a resistance. This is measured by the practical unit, ohm, and 
in alternating current topics is often called for precision's sake 
ohmic resistance. This is the resistance of Ohm's law, indicated 
in formulas by R, and is independent of the electromotive force 
and current. 

Self-induction, which when a current is increasing in strength 

manifests itself by counter electromotive force, increases with 

the current and therefore with the electromotive force. Counter 

electromotive force is a variable quantity in a circuit of fixed 

inductance. 

■p 
From Ohm's law expressed as I = __. we see that in a circuit 

±1 

of constant resistance the electromotive force must vary directly 
as the current. Therefore, as induced electromotive force varies 
directly with the current change, we can deduce an expression 
which will express it as a constant resistance, into which ex- 
pression current will not enter as a factor. Then in the expres- 
sion for the entire obstruction offered to an alternating or other 
type of varying current, we shall have two additive constituents. 
One is ohmic resistance, independent of current strength; the 
other is an ohmic equivalent of inductance, also independent of 
current strength. 

Ohm's law can be expressed as R =__!.. The inductance of a 

1 

circuit multiplied by the current change, which other things be- 
ing equal varies with the ultimate current strength, is equal 
to the counter electromotive force. As these two factors increase 
and diminish together, counter electromotive force divided by 

current strength is a constant quantity. By Ohm's law — = R 

or resistance. Hence we can express the effect of counter elec- 
tromotive force on a varying current, which calls it into ex- 
istence, by a constant resistance equivalent thereto in its action 
on such varying current. 

This resistance can be expressed in ohms, and is called re- 
actance. 



336 ELECTRICIANS' HANDY BOOK. 

By Ohm's law R =— . Therefore, R = '^^' where n is taken 
i nl 

as any multiple whatever. But by the law of self-induction a rate 
of change in a current will produce a definite counter electromotive 
force in a specific circuit. If such rate of change be multiplied by 
a factor, which may be indicated by n, the electromotive force in- 
duced by it will also be increased in precisely the same ratio, or n 
times. Calling the rate of increase of current I or nl as the case 
may be, the induced electromotive force will be B and nE respec- 
tively, and . — = = R. Reactance is therefore expressible in 

ohms. 1 *'-^ 

Ohmic Equivalent of Reactance of Inductance.— This numer- 
ical quantity depends on two factors. One is the inductance in 
henries of the circuit, and the other is the frequency of the alter- 
nations of the current. Calling inductance in henries L and fre- 
quency /, we have the expression for the value of inductance re- 
actance, A, in ohms: 

A = 2 ;f n^ or 6.28318 /L 
The numerical factor 6.28318 is 2 7t. 

Inductance Reactance in Subdivided Conductor.— The induc- 
tance of a copper wire varies very little for variations in its di- 
ameter. In round numbers a wire of 167,000 circular mils cross 
section has 80 per cent of the inductance of one of 42,000 circular 
mils and 70 per cent of the inductance of one of 6,500 circular 
mils. The resistance in these three wires would be approximately 
in the ratio of 4 : 16 : 100, the inductance as 70 : 80 : 100. The 
resistance varying inversely with the circular mils, increases 
in a much greater ratio than the inductance, and the discrepancy 
increases in more rapid ratio as the conductors are reduced in 
size. With sufficient subdivision the ohmic resistance would in- 
cease in so rapid a ratio, that the inductance could be taken as 
constant without any considerable error. 

Assume that inductance is unchanged by reducing the size of 
the conductor, and that we have a conductor of 1 ohm resistance, 
and at the given frequency of alternation possessing inductance 
whose effect is a reactance of 5 ohms. Assume that a current 
of 1 ampere is to be maintained. 
The graphic solution is first given. 



THE ALTERNATING CURRENT. 



337 



The perpendicular line, Fig. 234, is divided for ohms of 
resistance, the horizontal line for. reactance, which is the 
ohmic equivalent of self-induction. The diagonal A indicates 
the impedance. Suppose we substitute four wires of the 
same aggregate section, then each wire will have a resistance 
of 4 ohms, and by our assumption the same inductance and 
consequent ohmic equivalent. The impedance of a single con- 
ductor will be shown by the line P. But this single con- 
ductor carries only one-fourth the current, or one-quarter am- 




1 2 3 4 5 

Fig. 334.— Reactancb in Subdivided Conductor. 



pere, because there are four of them. Its length represents the 
total impedance of one of the new lines, and evidently is not four 
times as long as A, but is but a small fraction greater. There- 
fore one of the new lines with an impedance of 6.04 ohms (for 
6.04 is the length of R) has only one-fourth the current to carry 
that the original thick wire of impedance 5.1 ohms had to carry. 
The voltage drop in the thick line is by Ohm's law: 

5.1 X 1 = 5.1 volts. 
The voltage drop in one of the thin lines is: 
6.04 X 1/4 = 1.5 volts. 

But as the four thin lines are in parallel, there will be the 
same drop in each, or the subdivided main will carry the same 
current as the thick solid one at less than one-third the drop 
in potential. 

The assumption made that self-inductance is the same for all 



J 



338 



ELECTRICIANS' HANDY BOOK. 



wires is incorrect, but the increase is so slow that the principle 
is correctly illustrated. If accurately calculated, the result will 
be a little less favorable to the subdivided line. 

Capacity.— This is the third quality which may exist in an 
alternating-current circuit. It is the last of the three qualities 
spoken of on page 331. Its action upon alternating current is 
the reverse of that of inductance, as it reduces resistance and 
gives lead to the current. It is indicated by such diagrams as 
Fig. 235; inductance by such as Fig. 236; non-inductive resistance 
by such as Fig. 237. 

Reactance of Capacity. — If a condenser is connected in a cir- 



FiG. 335.— Symbol of Capacitt. 



Pig. 336.— Symbol of Inductance. 



Fig. 237.— Symbol of Non-inductive Resistance. 



cuit, it will open or break the circuit as far as a direct current 
is concerned. No current would pass, and the circuit would be 
blocked as effectually as if the wire were cut. But the circuit 
with a condenser in it is a closed circuit for an alternating cur- 
rent. Electricity may be said to be poured into it at one period 
and out of it at another, so that the alternating action is kept up 
as if it were a closed circuit. 

Just as resistance and inductance have each a twofold effect 
in an alternating current circuit, one upon the current intensity 
and the other on the phase relation of alternating current and 
electromotive force, so has capacity. Capacity increases current 
or reduces the resistance, or increases the conductivity of a cir- 



THE ALTERNATING CURRENT. 339 

cuit for alternating currents, and acts to give the current a lead 
over the electromotive force. Its action is exactly the reverse of 
that of inductance. Infinite inductance would reduce an alter- 
nating current to zero, while increase of capacity would diminish 
the reactance of a circuit so that an alternating current in it 
would be of increased strength. 

Ohmic Equivalent of Reactance of Capacity. — It is best to 
use the farad as the unit of capacity in the reactance formula. 
Capacity appears in the formula as the denominator of a fraction, 
so that capacity reactance would become zero if capacity became 
infinite. The formula is in form the reciprocal of the induc- 
tance reactance formula, page 336, with farads, indicated by K, 
substituted for henries. 

Calling farads of capacity K, and capacity reactance B, we have: 
1 1 



R=. 



2 TT/K 6.2S318/K 

This gives the value of capacity reactance in ohms for a cur- 
rent of frequency f with a capacity of K farads in its circuit. 

Impedance indicates the impeding effect exercised upon an al- 
ternating current by the combined ohmic resistance and reactances 
of the circuit through which it passes. A circuit always contains 
resistance, and may contain capacity and inductance. If it con- 
tains two or three of these qualities, the ohmic resistance it of- 
fers to the passage of an alternating current is made up of the 
combined effect of resistance and reactance; the latter may be of 
one or of both kinds. The combined effect is not due to simple 
addition because induction reactance and capacity reactance are 
opposed to each other, and each is in quadrature with resistance. 

Calling resistance R, inductance reactance A, and capacity re- 
actance B, we have as the value of impedance: 



Impedance = V R' + (A — B)^ 
If there is no inductance reactance, then A = 0, and the above 



by regular algebraic process reduces to VR" + B^. 

If there is no capacity reactance, then B = 0, and it reduces to 



VR' + A^ 

Electric Resonance. — This term is applied to the condition 
that obtains in a circuit when the inductance reactance, expressed 



340 ELECTRICIANS' HANDY BOOK. 

by 2;rfL, and the capacity reactance, expressed by ^ are 

27efK 
equal to each other. The formula for the impedance of a circuit 
containing resistance inductance and capacity is: 

Impedance = K- + (s tt /L — - — -^j 

If 2 icflu = = then the formula reduces to: 

Impedance = ^W or R. 

Electrical resonance in other words causes an alternating-cur- 
rent circuit to act as if it had only true ohmic resistance. But 
its capacity and inductance have not been annihilated, but only 
put into opposition with each other, and this brings about re- 
sonance. 

By Ohm's law we have E = R I. For the inductance of a cir- 
cuit the Ohmic equivalent of reactance must be substituted in 
the above formula. Then the value of I is determined by Ohm's 
law as if there were neither inductance nor reactance, and with 
that value of I, and substituting for R the ohmic value of induc- 
tance reactance or capacity reactance, the value of E for the in- 
ductance element and capacity element of the system are reached. 

Suppose that in a system fed by alternating current there is a 
condenser of 50 microfarads capacity (0.00005 farad) and that 
there is an inductance of 0.050 henry. Take the frequency at 
100 and the effective E.M.F. as 100 volts. The inductance react- 
ance is 2 7zr X 100 X 0.050 =: 31.4; the capacity reactance is 

- = — r= 31.8. Take the resistance at 2 

2 7f X 100 X U.000U5 0.( 514 

ohms. Then for the total impedance we have: Impedance = 



y'22+ (31.4 — 31.8)2 which is practically 2 ohms. By Ohm's law 
a current will flow through such a circuit expressed by: 

ior J-^= 50 amperes. 

A 2 

Neither of the reactances has been annihilated; they simply 
counteract each other's effects, but each acts individually the same 
as ever. The inductance reactance remains at 32 ohms nearly. 
Through it a current of 50 ohms has to pass. Therefore by Ohm's 



THE ALTERNATING CURRENT. 341 

law, E = I R, we have E := 50 X 32 or 1600 volts as the electro- 
motive force between the terminals of the coil embodying the 
inductance of the system. For the reactance an identical figure 
is obtained. Thus by resonance an original 100-volt electromotive 
force can generate in parts of a circuit a voltage many times 
greater. Fig. 238 shows the diagram of a portion of a circuit 
containing inductance and capacity. 

All the figures in the above calculation are approximate, deci- 
mals being omitted or restricted. 

The equation 2 7t f L= may be considered as expressing 

the condition of resonancy. It follows that if f and L are known, 
the value of K which gives resonancy can be calculated, and that 
if f and K are known, the corresponding value of L can be calcu- 
lated. This is done by the ordinary operations of algebra. The 
equation tells that if L is large K must be small, and vice versa, 
in order to bring about resonance. 

In a circuit in which electrical resonance exists the entire cir- 
cuit is not affected by it, but only the portions containing induct- 
ance and capacity. The circuit as a whole passes the current 
subject to Ohm's law, while the portion containing inductance 
and the other portion containing capacity work in concert with 
each other, and if in tune, as it is sometimes expressed, are the 
seats of high electromotive force. Damage to apparatus some- 
times ensues from this. While resonance eliminates the effects 
of the inductance and the capacity upon the circuit taken as a 
whole, it leaves each one unaffected in its action. The inductance 
still has its value in henries, the capacity still has its value in 
farads, and they retain their individual characteristics and power 
of reaction. 

Causes of Lag and Lead. — The effect of inductance in a circuit 
is to cause alternating current to lag behind the impressed alter- 
nating electromotive force which produces it. The lag, if the 
circuit possessed neither capacity nor resistance, would attain 
its highest possible value, which is 90° or quadrature. Induct- 
ance is the cause of lag. 

The effect of resistance in a circuit is to cause alternating cur- 
rent to tend to be in phase with the impressed electromotive 



342 ELECTRICIANS' HANDY BOOK. 

force. If a circuit possessed neither capacity nor inductance, the 
impressed electromotive force and current would be in perfect 
phase with each other. 

The effect of capacity in a circuit is to cause the current to 
lead impressed alternating electromotive force. This lead, if 
the circuit possessed neither inductance nor resistance, would 
attain its highest possible value, which, as in the case of lag 
above cited, is 90°, or quadrature. Capacity is the cause of lead. 

It follows that resistance acts in quadrature with inductance 
and capacity, and that capacity acts in direct opposition *o 
inductance. 

Summatioil of Alterna ing Quantities. — The combined effect 
of quantities acting additively in alternating manner, so that 
their alternations may be represented by a sine curve, cannot 



^wsmh 



Fig. 238.— Capacity and Inductance in a Circuit. 

always be expressed by simple addition. Suppose a sine wave one 
inch high represents the action of a certain alternating current. 
Next suppose that a second current is poured into the line, 
coinciding in phase, intensity, and form with the first. A wave 
of twice the height would result. The combined effects of the 
two currents could be expressed numerically by adding them 
together. 

It will be understood that whatever is said of current her^ 
applies also to electromotive force. Current and electromotive 
force alternate in exactly the same manner, and either can have 
its action represented by a curve of the sine type. 

Suppose now that the currents differed 180° in phase, as shown 
in Fig. 233. One would be positive in its alternation when the 
other was negative, one would exactly counteract the other, and 
the result would be zero. Suppose that the phases of the two 
currents differ 90° in phase. In some parts of their gycles they 



THE ALTERNATING CURRENT 



343 



co-operate, in others they resist each other, and a more compli- 
cated curve is the result. 

The values of two sine curves can be added together by draw- 
ing them and constructing a new curve. Its height at any point 
is determined by adding algebraically the heights of the original 
curves at that point. Distances below the base line are treated as 
negative. Fig, 239 shows another method. AF and A F' are the 
generating circles of two sine waves whose phase difference is the 
angle between A B and A B'. The two vectors are compounded as 
in Fig. 239, and with the new vector A B" a new generating circle 
is produced, from which the new curve is generated. The curve 




\^/ 



Fig. 239.— Summation of Sinti: Cubves. 



I is generated from circle F B D B, curve II from circle F' . . . , 
and the curve III is produced by adding I and II or by directly 
generating it from the generating circle B". . . 

Composition of Resistance, Inductance, and Capacity.. — Every 
circuit possesses these three qualities. Their combined effect 
may be found by a simple diagram, although where accuracy is 
required, mathematical calculations are essential. 

Let a horizontal line be drawn starting at an origin O and of 
length to represent the ohmic resistance of a circuit. The react- 
ance of inductance will be represented by a line at right angles 
to it, because the two are in quadrature. Draw the inductance 
line vertical and rising from the origin, and of length to repre- 
sent inductance reactance. The reactance of capacity is 180° 
removed from that of inductance, and hence is also in quadrature 



344 



ELECTRICIANS' HANDY BOOK. 



with resistance. The line representing it will start from the 
origin and extend vertically downward. 

There is nothing absolute about the position of these lines, 
except that they must be related to each other as shown. 

Each line or radius vector must be drawn of length to give the 
relative value in ohms of the reactance it represents. 

In the diagram, Fig. 239a, the line O R represents resistance, 
O I represents inductance, and O K capacity. Draw I D parallel 
to R and equal to it in length. The diagonal from to D or 
O D is the resultant of combined effect of resistance and induct- 




FiG. 339a.— CoMPOSTTTON of "Resistance, Inductance, and Capacity. 



ance reactance. Then from D draw a line D F parallel to O K 
and equal to it in length. The diagonal OF will give a line ex- 
pressing the combined effect of the two reactances and of resist- 
ance. 

Multiplication of Alternating Quantities. — The multiplica- 
tion of alternating quantities has to be done to find the power of 
a circuit in watts, because the latter unit is a product of electro- 
motive force by current, a volt by an ampere. The term volt- 
ampere signifies a watt. 

If an alternating electromotive force is multiplied by an alter- 
nating current, a product differing altogether in form and value 
from the additive or compounded result is obtained. This 



THE ALTERNATING CURRENT. 



345 



product is a curve of power, of volt-amperes or of watts. Its 
amplitudes indicate quantities of watts at the different periods. 

Power Curves.— The diagrams, Figs. 240 and 241, show each a 
curve of sines of electromotive force in full line, and one of cur- 
rent in dots. Multiplying their amplitudes together, new ampli- 
tudes are obtained, which give the curve drawn in dot and dash, 
which is the volt-ampere curve, curve of watts or power curve. 

When the current curve or the electromotive force curve crosses 




Figs. 240 and 341.— Multiplication of Alternating Quantities. 



the base line, its amplitude is zero. Therefore the amplitude of 
the power curve at this point must also be zero, because the 
product of a finite quantity, in this case the amplitude of the 
other curve at th-e same point, multiplied by zero is equal to zero. 
As the electromotive force is, in the case shown in the cut, out 
of phase with the current, for each cycle or period there are 
four zero factors. This brings the power curve twice as often 
to the base line as either of the original curves. It has twice 
the alternations of either of them. 

The system receives energy from the alternator during the 
time the power curve is above the base line. It receives energy 
in varying amounts whose measure is the amplitude of the curve 
at that point. It returns energ^^ to the alternator when below 



346 ELECTRICIANS' HAND^ BOOK. 

the line, measured as before for any instant by the amplitude of 
the curve at that point. 

The second of these diagrams. Fig. 241, shows the electro- 
motive force curve and current curve in quadrature with each 
other. This condition would be brought about by presence of 
inductance and absence of resistance in the circuit. The power 
curve in this case is half above and half below the line. It has 
twice the alternations of either of the other curves, just as before. 
It indicates the return of exactly as much energy as is received. 
In such a case no energy is expended on the line. It is the case 
of the wattless current. The portions of the curve above the line 
represent power received; those below represent power returned. 
The two are equal, and as they are opposed in action, the com- 
bined result is zero. 

Referring again to Fig. 227, the current and electromotive force 
curves are divided by vertical lines crossing the zero line at the 
intersections of the curves. Within the space I, E. M. F. ordi- 
nates above the line, which are positive, are multiplied by current 
ordinates below it, which are negative. The result is negative by 
algebra. Therefore the new curve for this division is below the 
line and negative. Within the space II, positive E. M. F. ordinates 
are multiplied by positive current ordinates, giving a positive 
curve or one above the line. Within the space III, positive cur- 
rent ordinates are multiplied by negative E. M. F. ordinates, 
bringing the combined curve below the line. Within the space 
IV, both- current and B. M. F. ordinates are negative. But by 
algebra negative multiplied by negative gives a positive quantity; 
therefore the combined curve is above the line here. This result 
is shown in Fig. 240. 

If B. M. F. and current curves are in phase with each other, all 
the multiplications are either of positive by positive or negative 
by negative, so that the new power curve is all on the positive 
side of the zero line. 

Two=Phase Current. — If two electromotive forces invariably in 
quadrature with each other are simultaneously produced by a 
generator, the currents produced may be distributed over four 
conductors, a pair for each current. The combination is called a 
two-phase current. It is illustrated in diagram, Fig. 242. The 



THE ALTERNATING CURRENT. 



347 



full line A. . . is one current, the dotted line B. . . is the other; the 
90° distances are marked on the diagram. 
Three-Phase Current. — If three electromotive forces invari- 




A B 

Fig. 243.— Two- Phase Current. 

ably 120° apart in phase are impressed on a six-wire circuit, what 
is called a three-phase current results. By special connections 
this current can be distributed by means of three or of four 




Fig. 243.— Three-Phase Current. 



wires. The diagram, Fig. 243, illustrates it. The full line A..., 
dotted line B..., and dot and dash line C... are curves of the 
three currents which really make up the so-called three-phase 
current. 



CHAPTER XX. 

ALTERNATING CURRENT GENERATORS. 

Generation of Alternating Current. — Alternating current is 
generated in dynamo-electric generators, which represent one of 
the simplest or fundamental cases of impressment of electro- 
motive force. The direct current dynamo is a step in the direc- 
tion of complication, as the alternating current dynamo with its 
simple collecting rings taking the current as it is generated is 
the simplest of all mechanical generators. For this reason some 
authors treat of alternating generators first and then of direct cur- 
rent generators. Some even make a discussion of the alternating 
current lead up to the direct current. 

Single=Phase Armature.— If a coil of wire with disconnected 
ends is rotated in a magnetic field with its axis of rotation sym- 
metrically placed as regards the lines of force, it will have im- 
pressed upon it at each revolution two electromotive forces of op- 
posite polarity. Its position may be to a considerable degree un- 
symmetrical as regards the field of force, yet the same will be 
true. Electromotive force to be utilized must produce a current. 
To utilize these pulsations, the ends of the open-circuit coil must 
be connected by an outer circuit. Upon the shaft carrying the 
coil are secured two copper rings insulated from one another 
and from the shaft. One terminal of the rotating coil is connected 
to one ring, and the other terminal to the other ring. A pair of 
brushes bear against the rings, one brush for each ring, and to 
these brushes the terminals of the outer circuit are connected. 
One terminal is connected to each brush, and the brushes are 
insulated from the frame of the machine. An iron core is placed 
within the coil, as in the direct-current dynamo, so that an arma- 
ture is constituted. 

The electromotive force produced by the rotation of the coil is 

348 



ALTERNATING CURRENT GENERATORS. 



349 



proportionate to the rate of change of the number of lines of 
force interlinked with the circuit by means of the coil. The elec- 
tromotive force passes from a maximum of one polarity to a 
value of zero, then to a maximum of the other polarity, back to 
zero, and then to its original polarity. This varying electro- 
motive force tends to produce upon the closed circuit a current 
varying in like manner as regards intensity, and reversing in 
direction as the polarity of the electromotive force changes. The 
reversing in direction of current must occur exactly as often as 
the reversing in polarity of the electromotive force, but lag or 




Fig. 344.— Elementary One-Phase 
Alternator. 




Fig. 245.— Multipolar Stator. 



lead will generally operate to prevent the two being simultan- 
eous, as they would be if there were no inductance or capacity 
in the circuit. 

The diagram of such a dynamo is given in Fig. 244. It is the 
simplest possible representation of an alternating-current gener- 
ator. The object and function of an alternating-current generator 
are to impress alternating electromotive force upon a circuit. 
What disposition is made of that electromotive force, whether 
it is made to produce a corresponding alternating current or not, 
and if it produces one how near it is to be to that which should 
be exacted by Ohm's law — all these are questions outside of the 
operation of the dynamo, except as regards its unvarying factors, 
such as capacity, inductance, and ohmic resistance. 



350 ELECTRICIANS' HANDY BOOK. 

Such an armature would produce a single alternating current 
on a closed circuit, and such a current is called a single-phase 
current. 

flultipolar Construction. — The alternating current as used in 
modern engineering practice must be of high frequency. A com- 
plete cycle would, with the bipolar construction just described, 
require a complete revolution. To give high frequency the arma- 
ture would have to be rotated at very high speed. If the poles 
are increased in number, a single rotation will give more cycles; 
in typical constructions one cycle is given per revolution for each 
pair of poles. If the field contains four poles, there will be two 
cycles per rotation; if it contains six poles, there will be three 
cycles, and so on. By increasing the number of poles a given 
frequency is obtained with fewer rotations of the armature per 
second. For this reason alternate-current generators generally 
have a number of poles, bipolar construction not being much 
used. Generators with more than two field poles are called multi- 
polar generators, and a multipolar stator is shown in Fig. 245. 

Grouping of Windings — The windings in alternators are gen- 
erally referable to groupings. The active conductors may gener- 
ally be assigned to groups, each group of approximately the width 
occupied by the face of a field pole, and there being a group of 
conductors for each pole. In a general way multipolar construc- 
tion by filling the circle of the armature with pole faces tends to 
make the distribution of conductors on the armature periphery 
even, but grouping can always be traced out for them. 

Principle of A lternate= Current Armature Winding. — This 
principle is that all active portions of the winding of an individ- 
ual armature winding must coincide in action at each instant, 
all co-operating to produce the same effect on the circuit. The 
direct-current armature winding with its commutator works in 
parallel of two for each pair of poles, while the alternating-cur- 
rent armature Avinding operates in series whatever is the number 
of field poles. The active conductors of an alternate current 
winding must be so joined that at any instant an electromotive 
force of uniform polarity shall be impressed upon all of them. 

Drum Armature Connections. — Suppose any number of pairs 
of north and south field poles arranged symmetrically around a 



ALTERNATING CURRENT GENERATORS. 



351 



drum-armatur-e core, mounted in bearings. Let the cylindrical 
surface of the core have conductors insulated from each other 
secured to it. If rotated in the multipolar field, each conductor 
will have alternating impulses of electromotive force impr-essed 
upon it, as many in one revolution as there are poles in the field,, 
and changing in polarization or "direction" in one revolution 
also as many times as the number of poles. 

Elementary Four=Pole Single=Phase Armature. — In Fig. 246 
a core is shown upon whose surface four conductors are placed. 
If rotated in a four-pole field, electromotive force will be im- 
pressed upon them of opposite polarity for every alternate con- 
ductor. The ends of these conductors are to be connected by wires 
or other conductors extending across the front and rear ends of 
the armature core. The ar- 
rowheads indicate the polar- 
ity of the electromotive ^ 
force, or the direction of 
current which it tends to 
produce in each conductor, 
at the Instant indicated. To 
have these currents coincide 
in direction for the entire 
winding, the front end of 
one conductor must be con- 
nected to the front end of 
a conductor one pole re- 
moved from it; the rear end 

of this one connected to the rear end of a" conductor one pole re- 
moved from it in the same direction, and the same system is car- 
ried out all around the circle. This brings the two ends of the 
windings out together. One end is connected to one collecting 
ring, the other is connected to the second collecting ring. Such a 
winding will give a single-phase alternating current. The action 
may be described as a zigzag action. The terminals of the wind- 
ing are subjected to the accumulated electromotive force im- 
pressed on the active conductors by the four poles of the field. 

Single-Phase Wave and Lap Winding. —An example of wave 
winding is shown in Fig. 247 in development. It will be seen 




Fig. 246. - Elementary One-Phase 

Drum Armature Wound for 

A FouB-PoLE Field. 



352 



ELECTRICIANS' HANDY BOOK. 




that the electromotive force impressed on each active conductor 
of the armature co-operates to produce a current in one direction 



Ite 



ALTERNATING CURRENT GENERATORS. 



353 



all through the windings. The active wires are spaced in accord- 
ance with the distance from pole to pole. In direct-current wind- 
ing the spacing is usually a little more or a little less than this 
distance. 

The next cut. Fig. 248, shows in development a single-phase 
lap winding. The spacing is regulated as in wave winding by the 
distance from pole to pole, and a uniform impressing of electro- 
motive force on all the active conductors is produced. 

If we trace the course of the conductors in two successive loops 
in the direct-current lap winding, we shall find our course a 
series of left-handed or right-handed turns as the case may be. 




Fig. 249.— Analysis op Direct Current Lap Winbinq, 




Fig. 250.— Analtsis of Alternating Current Lap Winding. 



but either left-handed or right-handed all the way around. If 
we start in the lines of Fig. 143 at the left hand and follow the 
line beginning at the left, we shall progress in a sort of spiral 
toward the right hand, always in the same sense. In this particu- 
lar case it will be against the movement of the hands of a watch. 

If the alternate current lap winding, Fig. 248, is traced out 
through its loops, we shall progress with the hands of a clock 
in one loop and against the hands of a clock in the next loop 
all the way around. 

The courses followed can be roughly shown, as in Figs. 249 
and 250. 

Ring Winding for Alternating Current. — In Fig. 251 is shown 
how a Gramme ring armature can be made to give an alternating 



354 



ELECTRICIANS' HANDY BOOK. 



current. For each pole of the field a single lead is taken from 
equidistant parts of the windings. Every second connection is 
taken to one collecting ring, and the others to the other collecting 
ring. Such an armature rotated in a multipolar field whose 
number of evenly-spaced poles is equal to the ring connections 
will develop a single-phase alternating current. The connec- 
tions operate to divide the windings into groups, one for each 
pole. 
Conventional Representation of Collecting Rings. — In Fig. 




Fig. 251.— Gramme Ring Connected 

FOB Single-Phase Alternating 

Current. 



Fig. 253.— Bipolar Single-Phase 
Alternating Current Pole 
Generator. 



251 we see the conventional way of representing collecting rings 
in diagrams. Two circles are drawn from the same center. One 
is of greater diameter than the o'her, and each represents a 
ring. These rings are really of identical size, but are conven- 
tionally represented as of different size, in order to distinguish 
between them. 

Pole Single= Phase Armature. — Armatures for alternating cur- 
rents are sometimes of the projecting-pole type. Poles project 
radially from them, and are wound in the same sense as the 
poles of the field. A direct current passed through the windings 
of such an armature would cause one projecting pole to be of 



ALTERNATING CURRENT GENERATORS. 



355 



north polarity and the next one to be of south polarity. One 
consecutive winding goes around all the poles in succession, and 
the induced single-phase current is taken from its terminals. 

In Fig. 252 direct current from an outside source may pass 
through the windings of the poles attached to the frame. The 
armature rotated in the field thus formed delivers current to the 
circuit connected to the collecting rings. The reverse may be 
carried out. Direct current may be supplied to the central poles 
by connections to the brushes. If the central part is rotated, al- 
ternating current can be taken 
from the windings of the 
frame poles. This construc- 
tion would give one cycle per 
revolution. 

In Fig. 253 the same system 
is indicated for four poles. 
This construction would give 
two cycles per revolution. 

Rotor and Stator.— In both 
the examples shown in the 
diagram. Figs. 252 and 253, 
electromotive force could be 
impressed on either the sta- 
tionary or rotary member of 
the machine. Whichever part 
it is impressed on is the arm- 
ature. The approved terminology for alternators calls the part 
which turns the rotor, whether it is a revolving field or armature ; 
and calls the part which does not turn the stator, whether it is a 
stationary armature or field. Yet the distinction of field and 
armature remains. The alternator can always show two parts, 
one the field through which a direct current is passed, the other 
the armature on whose windings alternating electromotive force 
is impressed. Either may be rotor. 

The general rule for single-phase windings is that armature 
and field are interchangeable. If a direct current is supplied to 
the field, electromotive force will be impressed on the arma- 
ture as the rotor turns. Again, if the armature be supplied 




Fig. 253.-rouB-PoLE Single-Phase 
Alternating Current Generator. 



356 



ELECTRICIANS' HANDY BOOK. 



with direct current, the field will have electromotive force im- 
pressed upon its windings. There is nothing practical in this, 
because the armature and field are generally wound with widely- 
different sizes and lengths of wires. One is wound to have good 
excitation from the source of direct current. The other is wound 
to give alternating electromotive force of the desired number of 
volts, under the effects of the field. It is obvious that the wind- 
ings are apt to be widely different. 

Inductor Alternator.— The principles of this type of alternator 
are shown in Fig. 254. The stator is both armature and field. 
The full line indicates the field winding through which a direct 




Fig. 354.— Inductor Alternator. 



current is maintained. It is wound around every second pole, so 
as to excite north and south polarity in them alternately. Thus, 
taking a north pole as a starting point, the one next to it would 
be without polarity, because the field windings do not go around 
it. The next pole would be a south pole, owing to the direction 
of the winding. This succession is kept up all the way around. 
A segment only is shown in the cut. The full line indicates the 
field winding, and the field poles are marked N and S. The neu- 
tral poles between the field poles are marked A A, and the arma- 
ture winding on them is shown by the dotted line. It is wound 
in the reverse sense on neighboring poles. 

The rotor carries heavy masses of soft iron B B, called induc- 
tors, each one wide enough to cover two poles on the stator and 
the interval between them. As the rotor turns, it changes the 



ALTERNATING CURRENT GENERATORS. 



357 



polarity of the neutral poles. Thus in the position shown, the 
left-hand neutral pole, acted on by the inductor extending from 
it to the south pole on its right, is polarized with north polarity. 
. The right-hand inductor polarizes the right-hand neutral pole 
above it with south polarity. When the rotor turns through an 
angular distance equal to one pole face and one pole interval, 
the opposite polarities are imparted to the neutral poles. In 
each revolution of the rotor the armature poles vary in polarity 
as many times as there are poles in the stator. 

The great advantage of this type of machine is that the wind- 
ings are stationary. A ma- 
chine with rapidly-rotating 
rotor carrying windings with 
it is not so solid a construc- 
tion as one in which the care- 
fully insulated windings are 
on a motionless part of the 
machine. 

Disk Windings.— This kind 
of armature has been used 
extensively in Europe, but 
not very extensively in this 
country. In preceding pages 
305, Figs. 203 and 205, disk 
dynamos have been shown, 
and in Fig. 255 the coils and 
collecting ring connections of a disk armature are shown. The 
arrows indicate the directon of the current. This direction 
changes during a rotation six times, because the armature is 
wound for a six-pole field. The disk armature does not need an 
iron core; it is so thin that the lines of force readily strike across 
it from pole to pole. 

Two=Phase Winding.— Suppose it was desired to send out twQ 
independent currents of equal periodicity, but differing as re- 
gards the phases of the electromotive force producing them, 
one electromotive force to be 90° behind the other. Two inde- 
pendent machines could be mechanically coupled. This would 
have to be so effected that the proper phase relation would obtain. 




Pig. 255.— Winding of Disk Arma- 

TUBB FOR Single-Phase 

A. C. Currents. 



358 



ELECTRICIANS' HANDY BOOK. 



which would involve setting the armatures so that one would be 
one half of a pole interval behind the other. The currents could 
be distributed on four lines of wire, two to each machine. The 
phase relation existing between the electromotive forces on the 
two circuits being invariable, the result would be called a two- 
phase current. An easier way to produce it is to have a second 
independent winding on the same armature. A single machine 
then produces the two-phase current. 

The cut, Fig. 256, shows the principle. The conductors A A 



B 








B 






( 


l£ 




; A 


1 

1 




A 


\ 


j_ 


_o 


Jl 


J_ 


i 


® 


C 


N 


) ( 


s 


^ ^ 


N 


^ -^ 
) ( 

' 


s 


^ 




) ( 




) 


























( 






\ 



Fig. 256.— Two-Phase Winding. 

are parts of a continuous conductor that goes all around the 
armature in every second groove. The windings B B do the 
same. The ends of each winding go to their own pair of collecting 
rings, of which there are four. The diagram shows rotor and 
stator as straight; in reality, each one is circular, and one lies 
within the other in the regular way. 

In the position shown, the windings A A are being acted on, and 
the current in them is indicated by the dot and cross symbols— 
the dots indicating current coming toward the observer, and the 
crosses indicating current going away from him. The conductors 
B B in the position shown have no electromotive force impressed 
on them; their sine curve is crossing the zero line. 

Either part shown can be stator. Usually it would be the arma- 
ture. 

Three=Phase Winding. — What has been said of the two-phase 



ALTERNATING CURRENT GENERATORS. 



359 



winding may be repeated with slight variation of three-phaso 
winding as shown in Fig. 257. The three windings are designated 
hy A, B, and C, and as no winding is in a neutral position, dots 
and crosses are put on all. The three represent three indepen- 
dent windings, and may deliver current to six collecting rings, 
a pair for each winding. 

Corresponding parts of adjacent windings are distant from each 
other two-thirds of a pole interval or one-third of two poles, which 
for a bipolar machine would be 120°. This fixes the condition 



! A 



! A r 



J^LfU 



/ 


N 


\ /, 


s 


r^ 


1 


N 


p^ Z 


s 


f^ 


( 




) c 


^ 


> \ 




> ( 




) 



































Fig. 257.— Threb-Phase Winding. 



that the currents induced shall be 120° different in phase from 
each other. 
Six-Wir© Connection of Three=Phase Alternator Winding.— 

The windings of a three-phase alternator may be variously con- 
nected. They may be treated as if they were windings of three 
separate machines, in which case two conductors would be as- 
signed to each of the three outer circuits which they could sup- 
ply. This would give a total of six conductors to be led through 
the district. Almost always other systems are used, which enable 
the distribution to be effected with three or four wires. A six- 
ring collector system is shown in Fig. 258. 

Y or Star Connection.— This connection requires four wires to 
distribute the power from a three-phase alternator — three active 
and one neutral wires. The latter passes current when the bal- 
ance is disturbed, exactly like the neutral wire in the three-wire 



360 



ELECTRICIANS' HANDY BOOK. 



system, of parallel distribution. The connections are made in the 
machine and on the outer circuit. 

The three windings of a three-phase alternator can be taken 
as beginning at three adjacent points on the armature. From 
these points collector-ring connections would be made were the 
six-wire system in use. For the Y system three of these ends, 
symmetrically distributed with reference to each other, are con- 
nected together, and one lead is taken from them through the 
district, which is the neutral lead. From each of the other ends 

of the three windings a lead is 
taken, thus giving a total of four 
leads. 

In the utilizing of the four 
mains, each lamp or other appli- 
ance is connected from one of the 
active wires to the neutral wire. 
The balance is kept as true as 
possible by taking the same 
amount of power from each act- 
ive lead. If exactly the same 
amount is taken, the neutral wire 
carries no current. 

The development of a Y wind- 
ing is shown in Fig. 259. There 
are three windings, A, B, and C. The A winding begins at A^ and 
ends at A4; the B winding begins at Bi and ends at Bj the C 
winding begins at Bi and ends at B4. The six ends which might 
be connected to six independent line wires are A, B, C, A4, B^, and 
C4. For the Y connection each second end is connected to the 
neutral wire. In the development these alternate ends are Ai, Ci, 
and B4. The remaining ends A4, C4, B^ are connected each to one 
of the active wires. If the course of the current is examined by 
the rule given on page 210, and carried out in Fig. 259 by the ar- 
rowheads, it will be seen that a strong downward current in Ai is 
balanced by weaker upward currents in B4 and Ci. The relative 
strength of the currents is due to the strength of the field 
through which they are moving, and Ai is evidently in a stronger 
field than either B4 or C,_. A strong current goes upward to the 




Fig. 358.— Six-Ring CoLiiBCTOB 
FOR Alternator. 



r^LTERNATma CURRENT GENERATORS. 



361 



upper line, whicli line indicates a collector ring with brush A, 
while weaker currents go down from the other collector rings. 

Delta or flesh Connection.— Taking the three windings as be- 
fore, a first and last end can be assigned to each. Thus in tne 




Fig. ^59.— DBVEIiOPMBNT OF T CONNECTIONS. 

Y connection it may be taken that the three interconnected ends 
joined to the neutral wire are first ends, and the three ends with 
separate conductors are the last ends. For delta connection the 
three windings are joined in series. The last end of one winding 
is joined to the first end of the winding next to it in phase (120° 






C C 

Figs. 360, 261, and 263.— Y, Delta, and Combination Connections. 

removed in phase). The last end of this second winding is 
joined to the first end of the third winding, and the last end 
of the third winding is joined to the first end of the first wind- 
ing. From each junction of first and last ends a wire is led 
through the district which is to be supplied, a total of three 
wires, there being no neutral wire. 



362 ELECTRICIANS' RANDY BOOK. 

Line Connections. — The appliances on the line may be con- 
nected from wire to wire, so as to maintain the delta distribution 
over the working circuit, or the Y system may be used with a delta 
system at its junction, so as to dispense with a neutral wire. The 

Y connection is shown in Fig. 260, the delta connection in Fig. 261, 
and the combined Y and delta connection in Fig. 262. 

Neutral Wire in the Y System. — This wire is usually treated 
as a part of the system requisite to its operation. It can be sup- 
pressed if the appliances on the three divisions are evenly bal- 
anced, the case being precisely analogous to that of the neutral 
wire in the three-wire system of distribution, except that it is 
a case of one neutral wire for three active wires and not of one 
neutral for two active wires. It is obviously impossible to secure 
such distribution in ordinary practice, so that naturally the 
fourth wire has come to be regarded as a necessary part of the 
connections. An interesting illustration of the properties of the 

Y connection has been made by causing three carbons to take the 
place of the three limbs of the Y and producing an arc at the 
junction, the carbons being drawn apart, as to cause a triple arc 
to strike. It was maintained without any neutral wire. Another 
experiment was the lighting of a triple-filament lamp, three lead- 
ing-in wires connecting to filaments joined at their ends Y fashion. 
This lamp was ignited without any return wire. 



CHAPTER XXL 



ALTERNATING CURRENT MOTORS. 



The Induction flotor. — This is a motor whose action depends 
upon the induction of electro-magnetic polarity in an armature 
wound with a re-entrant coil, or with a coil whose members are 
connected in parallel. The coil must not be an open one. The 
alternating current in the field induces currents in the windings, 
which induced currents produce polarity in the core of the arma- 
ture. The polarity of the armature 
being due only to induction, gives its 
name to the motor. 

The Rotary Field.— The produc- 
tion of the rotary field is the prin- 
cipal reason for the generation of 
polyphase currents. By means of 
this invisible transferring of mag- 
netic polarity around a circle, one 
principal type of the alternating-cur- 
rent motor is operated. 

The cut. Pig. 263, shows four coils 
of wire. Let the coils B B receive 
an alternating current, while the coils A A receive another cur- 
rent in quadrature with the first. The result will be that when 
the current in B B is at its maximum, the current A A. . will 
be of zero intensity. Then as the current in B . . decreases, that 
in A... will increase. When the B current is at its maximum, 
north and south magnet poles will be established on a horizontal 
axis passing through the center of the B coils. The A coils when 
active will establish poles on an axis perpendicular thereto. Poles 
at intermediate points will be established when current is pass- 
ing through all four coils. The result of the arrangement is that 




B B 

Fig. 363.— Rotary Fieij) 

Coils. 



364 



ELECTRICIANS' HANDY BOOK. 



a north and south pole are kept traveling around the circle by 
the action of the alternating currents in quadrature with each 
other. Such currents constitute a two-phase alternating current. 

The change of one current from one maximum to the other 
takes place perhaps one hundred times in a second. Hence the 
resultant poles of the field whirl around it with great rapidity. 
The first Niagara alternators give a two-phase current with twen- 
ty-five periods in a second. These produce a rotating field that 
has fifteen hundred rotations per minute. 

Three such coils of wire with a three-phase current would give 
a rotary field. 

riagnetic Needle in a Rotating Field. — A compass needle piv- 
oted in the rotating field with 
its axis of suspension coincid- 
ing with the axis of rotation 
of the field would whirl 
around v/ith the speed of the 
field once it was started. 
Such an arrangement would 
not be an induction motor. 
An induction motor is one in 
which the rotating field in- 
duces currents in the arma- 
ture, and under the com- 
bined effect of the field and 
armature excitation the arma- 
ture revolves. 

Armature in a Rotary Field. — If instead of a magnetic needle 
a cylindrical laminated armature core wound with a re-entrant 
coil as shown in Fig. 264 is mounted on bearings in the field, 
it will rotate. This it will do because the alternating cur- 
rents will induce currents in its wires. This they do directly by 
their rotary field of force. This whirls around, and thus its 
lines of force are cut by the windings of the armature core, 
which cutting induces a current in them, producing north and 
south poles in the core. The core with its windings is mounted 
in journals and rotates as did the magnetized needle, but with a 
very important distinction. To establish in the core the polarity 




Fig 



L— Two-Phase Rotating Field 
AND Armature. 



ALTERNATING CURRENT MOTORS. 



365 



described above, lines of force have to be cut by its windings. 
Therefore it drops behind in its revolutions, and turns from one 
to five per cent, ten per cent in small motors at full load, slower 
than does the rotary field. If it by any means was made to 
synchronize with the field, it would have no induced polarity such 
as described, and no pull or torque would be exerted upon it. 
Therefore it constantly falls behind. The amount of this falling 
behind is called its slip. 

The generation of a three-phase current and the operation by 
it of an induction motor are shown in diagram in Fig. 265. By 




Fig. 265.— Thrbe-Phase Generator and Induction "Motor. 



following the figures it will be seen that the stator of the motor 
receives the identical currents induced in the stator of the gen- 
erator; but the poles of the generator stator travel around it. 
Consequently, a rotary field is produced in the stator of the 
motor. 

Three=Phase Induction Motor.— The diagram, Fig. 266, repre- 
sents a four-pole three-phase generator driving such a motor. 
The generator has twelve armature coils, three sets marked ABC 
for each field pole, giving a three-phase current. They are con- 
nected in Y combination. The left-hand diagram represents the 
generator. The field is the rotor. The motor, also with twelve 



366 



ELECTRICIANS' HANDY BOOK. 



coils, marked as in the motor, and Y-connected, is indicated by 
the right-hand diagram. The motor and generator are connected 
by three wires, a, & and c. The fourth wire is omitted because 
it would have no load to carry. The capital letters on the arma- 
ture of the generator enable the course of the windings to be 
followed. ■ 

The three-phase current produces a rotary field as the two- 
phase current does on the same general principle. The lag of 
the currents beliind one another acts to cause the poles resulting 
from the combined action of the coils to rotate around the field. 
These poles may be the resultant of two or of three windings; 
they are never due to one only in the three-phase motor. 




Fig. 366.— Fottr-Pole Thrbe-Phase Generator and Induction Motor. 



Induction Motors.— Motors constructed on the above principle 
are called induction motors. One of the most striking features 
about them is the fact that the coils on the armature, which is the 
rotor, are self-contained, have their terminals connected so that 
the winding is purely re-entrant, and have no outside connection 
whatever. A General Electric Company induction motor is shown 
in Fig. 267. 

Rotary and Revolving Field. — What has been described is the 
rotary field. In it the rotary action is purely electrical, there is 
no rotation of any part of the mechanism. A revolving field is 
another thing — it is a field which turns around an axis like a 
wheel. It is often used in alternating-current generators. There 



ALTERNATING CURRENT MOTORS. 



367 



is danger of confusion in the use of these two terms, and the 
meaning of each should be grasped, so as to keep the distinction 
between them. 

By a simple modification of mechanical structure, a rotary field 
may be mounted on journals and the armature may be fixed. In 
such a case the field becomes the rotor, and is really a combined 
rotary and revolving field. 

Starting Torque. — Polyphase-current induction motors have a 
starting torque, which single-phase synchronous motors are desti- 




FiG. 36T.— Induction Motor with Sqctrreij Cage Armattjri!. 



tute of. This feature has made polyphase currents the favorite 
type of alternating currents. 

Squirrel Cage Armature. — This is a favorite type of armature 
used on induction motors. It consists of a laminated core, with 
straight conductors of copper lying in longitudinal grooves or 
holes as close to its surface as possible. The ends are connected 
to two rings of copper. The windings thus provided have been 
aptly compared to a squirrel cage, and the name has been defin- 
itely adopted for them. A simple form is shown in Fig. 268. 

Starting Resistances are used to develop starting torque. It 



368 ELECTRICIANS' HANDY BOOK. 

is proved in the analytical discussion of the induction motor that 
at starting the torque is proportional to the rotor resistance. 
Resistances are provided for changing the resistance of the rotor 
windings. In the General Electric Company's form L motor, a 
wound armature is used with distinct circuits instead of a squir- 
rel-cage armature. The terminals of the circuits come out in the 
center of the armature, and are connected to each other through 
resistance grids. The grids have contact points, and a shoe 
worked from outside the motor by a lever slides back and forth, 
so as to cut resistance in or out as required. 

Many arrangements of starting resistance have been used by 
different makers. 

Starting Compensator.— This is also used in starting the in- 




FiG. Ji68.— Squirrel Cage Armature. 



duction motor. It is a transformer containing a single coil which 
takes full line voltage. It has one or more taps, and by connect- 
ing the motor to one of the taps a reduced voltage is obtained 
for starting. When the motor reaches nearly full speed, it is 
thrown from the tap directly into the circuit, so as to get full 
voltage. The change is effected by a switch working in oil situ- 
ated in the base of the compensator. The motor to be used with 
this apparatus has the simple squirrel-cage armature, as there is 
no change of armature resistance to be brought about, and it is of 
simpler construction. It is applicable where the motor is not 
obliged to start with full load, and where there is no objection 
to the use of a large starting current. 



ALTERNATING CURRENT MOTORS. 369 

Lenz's Law and the Induction Motor.— Lenz's law applies to 
this motor. The rotary field as its poles move induces currents 
in the armature opposing the motion of the fields. This motion 
while not mechanical has exactly the effect of a mechanical move- 
ment of the poles. Currents opposing the motion, with their 
action increased by the iron of the core, cause the armature to 
rotate exactly in accordance with the law. 

Construction of Induction Motors.— Laminated cores for field 
and armature are much used, such as have already been illus- 
trated previously. The windings of the armature, if of the squir- 
rel-cage type, are not necessarily insulated from the frame. The 
motor with starting resistance may give a starting torque 50 
per cent greater than the full load running torque with about the 
same excess of current. They are made of high horse-power as 
well as of smaller power. 

The Synchronous flotor. — If two single-phase alternators are 
connected together in one circuit, one may be driven by power 
so as to impress alternating electromotive force upon the line 
with accompanying current. The other alternator receiving cur- 
rent from the line if it is once started into motion so as to cor- 
respond with the alternations of the other, will continue moving 
and be a motor. For each alternation of current an identical 
alternation is involved in its operation; the two machines work- 
ing together harmonize exactly in the time of their alternations, 
and are said to be in synchronism. The motor machine is a 
synchronous motor. 

When current and electromotive force generated by its motion 
harmonize in direction, an electric machine of the dynamo type 
in which such condition exists is a generator. In other words, 
such condition can only exist in a system to which power is ap- 
plied — can only exist in a dynamo whose armature is turned 
by power. If mechanical energy is expended on an alternator, 
electromotive force and current harmonizing with each other 
will be the result. 

The generation of electromotive force opposed to the current 
received by a dynamo indicates that that dynamo is a motor — is 
giving out no electrical energy, but is absorbing it and is giving 
out mechanical energy. Therefore, if an alternator has its cur- 



370 



ELECTBICIAN8' HANDY BOOK. 



rent opposed to the electromotive force its motion generates, it 
becomes under proper conditions a motor. 

The synclironoiis ohe-phase motor is based on these principles. 

Condition of Operation. — The cut, Fig. 269, shows two curves, 
one of electromotive force, and one of current. The current 
lags. The current and electromotive force oppose each other in 
the section marked I, are together in II, opposed in III, and to- 
gether in IV. An alternator producing a current and electro- 
motive force of these relations would during the periods I and 
III give out mechanical energy and absorb electric energy and 




Fig. 369.— CtTBRENT and Electbomotive Forcb Curves. 



be a motor. During the periods II and IV it would absorb mech- 
anical energy and give out electric energy and be a generator. 

If the lag was 90°, or in quadrature, the periods I and III 
would be equal in all ways to II and IV, and the machine as far 
as its electrical functions were, concerned would absorb no mech- 
anical energy and give out no electrical energy. It would be in 
a wattless condition. If the lag exceeded 90°, periods I and III 
would be larger than II and IV, and the machine would absorb 
electric energy and give off mechanical energy and would become 
a synchronous motor. 



ALTERNATING CURRENT MOTORS. 



371 



There need be no structural difference between the generator 
of a single-phase alternating current and the synchronous motor 
driven by it. Whether a machine is one or the other is a ques- 
tion of phase relation of volts and amperes. If the two identical 
machines of the single-phase alternating-current type are con- 
nected electrically, and one is rotated by power as a generator 
and the other by any means is caused to rotate at the same 
speed, the latter becomes a motor, and will thereafter rotate at 
the identical speed of the generator and be driven by it as a 
synchronous motor. In the generator the electromotive force 
and current will be nearly in phase with each other. In the 




Fig. 370.— Single-Phase Generator and Synchronous Motor. 



motor counter electromotive force will be generated, and will 
almost exactly oppose the current. In the generator the curves 
of current and electromotive force will be almost in phase, and in 
the motor the counter electromotive force will be almost 180° 
different in phase. 

Single=Phase Synchronous Motor. — A single-phase generator 
and motor connected are shown in the diagram. Fig. 270. They 
are of identical construction. The current generated by the 
generator is indicated by the heavy arrows. This current causes 
the rotor of the motor to turn in exact synchronism with the 
generator. The rotation of the rotor of the motor generates 



372 



ELECTRICIANS' HANDY BOOK. 



counter electromotive force. The polarity of this is indicated 
by the lighter arrows. 

For synchronous rotation the conditions of phase in the two 
armatures must be exactly opposite, if one is to be a generator 
and one a motor. Therefore, torque is not to be looked for until 
synchronism is attained. For this reason a synchronous single- 
phase motor has no starting torque, and has to be started in 
some way until it moves as fast as the generator. After that is 
done it will go on exercising torque, and absorbing electrical 
and developing mechanical energy. 

To start it the current is divided, and one branch by a capacity 




Fig. 271.— Three-Phase Generator and Synchronous Motor. 



or inductance is thrown as nearly 90° out of phase with the 
other as possible. The two leads are then connected to the ma- 
chine and establish a rotary field, and the synchronous motor is 
thus converted into an induction motor. It is speeded up, as it 
now has starting torque. When going fast enough the inductance 
is cut out, and it continues in motion as a synchronous motor. 
Synchronous Polyphase Motor.— As far as revolving is con- 
cerned, a polyphase generator and motor may be identical. In 
a rotating field magnet permanent poles are maintained by a 
direct current. The polyphase alternating current is passed 
through the windings of a stationary armature. This creates 
in it a rotary field. The condition is illustrated in diagram ih 
Fig. 271, a permanent magnet representing the electro-magnet of 
the description. The generator on the left produces a rotary 



ALTERNATING CURRENT MOTORS. 



373 



field in the motor, which causes its rotor, which is its field mag- 
net, to revolve in exact synchronism. 

The stator and rotor may be reversed in the construction. 

Self- Starting Synchronous Motor. — To make a polyphase 
synchronous motor self-starting, the following arrangement is 
sometimes adopted. 

Copper bars connected at '^heir ends are bedded in the faces of 
the pole pieces of the field magnet. The rotary field acts upon 
these, and induces current in them exactly as in the induction 
motor. To start the motor, the direct-current field circuit is 
opened, and the alternating circuit is closed. The motor is now an 




Fig. 272.- Synchbonotjs Motor Rotor with Starting Armature. 



induction motor, and the rotor begins to turn. It is given no 
load, so that the rotor soon turns almost at the speed of the 
rotary field. The direct current is now turned on, and the motor 
becomes a synchronous motor. The elements of the induction 
motor are still present, but no torque is exercised by them be- 
cause there is no slip. 

The same principle is carried out by mounting on the same 
shaft with the synchronous armature a smaller induction-motor 
armature. When in place each armature lies in its own field, 
and the induction motor is used to start and to bring up to syn- 
chronism the larger armature of the synchronous motor. When 



374 ELECTRICIANS' HANDY BOOK. 

this is effected, the synchronous motor takes up the load, and the 
induction motor ceases to act. Fig. 272 shows the armature of a 
•synchronous motor with the squirrel-cage armature of the start- 
ing induction motor on the right-hand end of the shaft. 

In the above lines the use of direct current and of alternating 
current for the motor has been spoken of. This refers to the 
field and armature currents respectively. An alternating-cur- 
rent generator has its field excited by a direct current, and gen- 
erates an alternating current from its armature. An alternating 
current synchronous motor goes a step further, as it has to be 
connected to two distinct circuits for its operation, each one sup- 
plying power. One circuit possesses direct current, which excites 
the field; the latter may be rotor or stator. In the diagrams 
it is shown as the rotor, and to avoid complication a permanent 
magnet is used as its representative. The other circuit, entirely 
distinct from the first one mentioned, passes alternating current 
to the armature windings. This is the true power circuit, cur- 
rent from which actuates the machine. In the diagrams the 
armature is shown as the stator, but the relation of stator and 
rotor can be changed. 



CHAPTER XXII. 

TRANSFORMERS. 

Basis of Transformer Construction.— If a current passes 
through a conductor, it establishes around it a field of force. 
Energy is expended in producing the field, but none in maintain- 
ing it. If a second wire or conductor lies parallel to the first 
during the time that the field of force is being built up, electro- 
motive force will be impressed upon it by the growth in number 
of the lines of force. This electromotive force will be of such 
polarity that it will tend to produce a current in the opposite di- 
rection to the original 
current. If the other cur- ^.^ 

rent weakens, energy will I ■—-, q bQ 

be drawn away from the 
field, and the electromotive 
force impressed upon the 
neighboring wire will be 
of the reverse polarity. 
Current is only produced 
during the period of change 

of intensity of field. The transformer contains two coils of wire 
insulated from each other. One, the primary, receives varying 
electromotive force; the other, which is the secondary, has elec- 
tromotive force impressed upon it by variations in the current 
passing through the primary. 

In Fig. 273 C represents a bundle of iron wire wound with two 
coils of insulated wire. The circuit from one coil, which is of 
small relative length and large current capacity, contains a bat- 
tery a and key &. The other coil of long fine wire has on its 
outer circuit c' c' two electrodes d d. On depressing and releasing 
the key, a spark will jump across the air space between the two 

375 




Fig. 373.— Action of a Tbansfobmeb. 



376 



ELECTRICIAN8' HANDY BOOK. 



electrodes, if all proportions are right. The first-named coil is 
the primary; the other is the secondary. 

The Object of a Transformer is to receive a given alternating 
voltage from an alternator delivered at one pair of terminals, 
and to deliver at another pair of terminals a different alternat- 
ing voltage. The transformers seen on house fronts and power 
line poles may have a comparatively fine wire deliver a small 
current at 1,000 to 6,000 volts potential to their primary terminals, 
while from their secondary terminals a current twenty to one 
hundred or more times greater is taken off with a potential 
difference at the secondary terminals of 50 or 60 volts only. 

A small copper wire might thus deliver a li/4 -ampere current to 
a transformer with 6,000 volts between the primary terminals. 




Fig. 274.— Alternator and 
Converter Relations. 




Fig. 374a.— Ring Transformer. 



This would be about 10 horse-power. But if this 10 horse-power 
had to be delivered with only 50 volts potential difference be- 
tween the primary terminals, the wire would have had to be of 
twelve times the cross-sectional area, and consequently of twelve 
times the weight, and approximately twelve times the cost. 

Choking. — Another function is performed by transformers. 
The current passed through them between their primary ter- 
minals is almost nothing if none is taken from the secondary. 
Hence they act to "choke" or hold back the current when de- 
sired without any considerable ensuing loss of energy. 

The construction is simplicity itself. The apparatus is so sim- 
ple and efficient that it appeals to the electrician as one of the 
most perfect of all electrical appliances. There are no moving 



TRANSFORMERS. 



377 



parts to wear out, except in a special type of transformer, and 
its action is absolutely automatic and perfect. 

Sylvanus P. Thompson very aptly says that a transformer 
may "be regarded as a dynamo with stationary field and armature, 
in which the alternating magnetism of the iron coil induces the 
desired current in the secondary coil, representing the armature. 

The Limitation of a Transformer 
is that it has to hav-e a varying cur- 
rent; practically, it is used .only on 
alternating current circuits. It pro- 
duces a secondary alternating current, 
which can be made to give a direct 
one by special mechanism. 

The Principle of a Transformer is 
shown in diagram in Fig. 274. An 
alternating current from an alternator 
on the left goes through the primary 
coil, wtich is wound around a sort of 
iron ring. Another coil entirely dis- 
connected from the primary is also 
wound around the ring; this is called 
the secondary coil. A ring trans- 
former with adequate coils is shown in 
Fig, 274a. ^s current goes back and 
forth in the primary, it produces lines 
of force, in the iron core principally. 
As the current starting from zero in- 
creases to a maximum, the lines of 
force increase in number, and are of 
polarity corresponding to the direction 
of the current. As the current re- 
cedes to zero the lines of force die away, and as the current goes 
to a maximum in the reverse direction, lines of force of opposite 
polarity to the first are produced. These changes in intensity 
and polarity of the field impress upon the secondary an electro- 
motive force varying from zero to maximum, and of constantly 
changing polarity. If there are ten times as many turns of wire 
iij the primary as tksre are in the secondary, the electromotive 




Figs. 275, 276, and 277.— La- 
minate d Shell Type 
Transformer Cores. 



378 



ELECTRICIANS' HANDY BOOK. 



force impressed on the secondary will be one-tenth that in the 
primary coil. The direct proportion of voltage impressed to 
relative number of turns will hold for all ordinary conditions. 

Shell or Jacket Type Transformers are those in which the 
coils are surrounded by masses of laminated iron. The material 
of the cores has to be of metal of good quality and quite thin. 
Insulation of some kind is used between the plates out of which 
the core is built up. 

The cuts, Figs. 275, 276, and 277, show the construction of mod- 



« 



Fig. 278,— Section ot a Shell Type Transformer. 



ern transformer cores, which are built up from the plates after 
the coils have been wound upon a form. The plates in the ex- 
ample shown are cut in such a shape that they can be pushed into 
the openings of the coils. i 

The primary and secondary coils can be wound on top of each 
other or side by side. The cuts. Figs. 278 and 280, show the coils 
on top of each other. 

Step=Up and Step=Down Transformers. — If the transformer 
raises the voltage of a system, it is called a step-up transformer; 
if it lowers it, its more usual service, it is called a step-down 
transformer or a transformer without any qualification. 



TRANSFORMERS. 



379 



Ratio of Transforination.— The ratio of voltage impressed on 
the primary to that impressed on the secondary in the working 
of the transformer, as determined by the relative numbers of 
turns of wire in each, is called the ratio of transformation. It 

secondary turns 
is expressed by a fraction : ■ and is often desig- 



nated by k. 
Shell Type Transformers. 



primary turns 



-The construction of the working 





Fig. 379.— Shell Type 
Transformer. 



Fig. 280.— Section op Shell 
Type Transformer. 



parts of a typical shell type transformer is shown in Figs. 279 
and 280 in section and elevation. The apparatus is a. transformer 
of the shell or jacket type, so called because a hollow laminated 
mass of iron, electrically speaking its core, surrounds the coils 
of the transformer. In the section the coils^ are seen imbedded 
in the hollow core. In this particular coil, the coils primary and 
secondary are wound separately and placed one above the other. 



380 



ELECTRICIANS' HANDY BOOK. 



Another shell type transformer with coils partly exposed is shown 
in Fig. 281. 

Core Transformers. — Transformers whose core is surrounded 
by the insulated primary and secondary coils are thus named. In 
Figs. 282 and others such coils are shown. In Fig. 283 the con- 
struction of such a transformer is 
shown, and in the next cuts, Figs. 
284 and 285, another form is illus- 
trated. The ring transformers 
shown in Figs. 274 and 274a are 
really core type transformers, al- 
though the term is usually applied 





Fig. 383— Cores of Core Type 
Fig. 381. - Shell Type Transformer. oil-Cooled Transformer. 

to those with straight cores, as the term ring transformers covers 
the other case. 

Disk=Wound Transformers.— Sometimes the coils are in a 
number of sections wound separately into disks and piled one 
on top of another in alternation, as shown in Figs. 283 and others. 
By connecting the sections in series or in different parallel con- 
nections, the primary can be made to serve for a voltage of vary- 



TRANSFORMERS. 



381 



ing amount, and the secondary can be connected to give different 
potentials. A series connection of the sections is used for the 
high voltages, and parallel connection for the low voltages. 

Pancake Coils. — Coils such as those shown in process of con- 
struction and completed in Figs. 286 and 287 are called pancake 
coils. They are insulated, taped, 
and shellacked so as to be quite 
strong. Such coils are often 
wound of copper ribbon as wide 
as a coil is high. The coils illus- 
trated are used in shell-type trans- 
formers cooled by air blast. 





Fig. 383.— Constbuction of a 
Core Transformer. 



Fig. 284.— Core Type Oil-Cooled 
Transformer. 



The Auto=Transformer consists of an iron core wound with a 
single coil which virtually constitutes the primary and secondary. 
The secondary circuit is taken from it at two points; one connec- 
tion is made at one end of the coil, the other at an intermediate 
point. The portion of the coil comprised between these points 
may be of wire of extra thickness. It represents the secondary 
coil. The voltages will be to each other as the total turns in 



382 



ELECTRICIANS' HANDY BOOK. 



the coil to those in the secondary portion of the winding. It 
may be a step-down or step-up transformer. In the latter case 
the short section of coil is connected as the primary. 

A similar connection is sometimes made to the secondary coil 
in the three-wire system as applied to the working circuits, which 
are the secondary circuits, of alternating current systems of dis- 




FiG. 285.— Coils and Core 

OF Core Type Oil-Cooled 

Transformer. 



Fig. 386.— Manufacture of Pancake 
Coils. 



tribution. Three wires are connected to the secondary, one in the 
center and one at each end. If a voltage of 220 is given by the 
secondary, then 110 volts will be formed between each end lead 
and middle lead. The centrally-connected wire is the neutral 
wire. This arrangement supplies current on the two-wire system 
until points are reached where it i^ to be used. At these points 
the transformers perform a double function, changing voltage and 
instituting a three-wire distribution. 



TRANSFORMERS. 383 

Action of the Transformer. — When the secondary circuit of 
a transformer is open, the inductance acts to keep back the cur- 
rent in the primary, and the transformer becomes virtually what 
Is called a choke coil. Some electric energy is wasted upon it, as 
it is not absolutely without current and the full voltage must be 
expended. When the secondary circuit is closed, a change of 
current intensity in the primary sends a current through the 
secondary, but in the opposite sense. Inductance is due to the 
energy required to increase the intensity of a field of force. The 




Fig 287.— Pancake Coils. 



primary sends a current of changing intensity in one direction, 
which produces lines of force through.the core of the transformer 
when left to itself, and as it expends energy on doing so is 
choked back. But if the secondary circuit is closed, a current in 
the reverse direction goes through it, and demagnetizing to great- 
er or less extent the core of the transformer, facilitates to that 
extent the passage of a current through the primary. 

A closed secondary circuit causes current to go through the 
primary; with an open secondary only a very small current can 
pass through the primary. 

Transformers must have as good permeance as possible, and 



S84 ELECTRICIANS' HANDY BOOK. 

hysteresis being a source of loss of energy must be avoided by 
the selection of an iron with low hysteretic coefficient, and by 
the use of laminated cores. 

Heat in Transformers. — Transformers become heated when in 
use, partly from the eddy currents in the masses of metal of 
which they are constructed, partly from the current in their 
coils. Cooling of some sort has to be adopted. For small coils 
this is effected by the circulation of air about them and by the 
natural radiation of heat. 

Outdoor transformers are generally of the smaller sizes, and 
frequently the above agencies are depended on to cool them. The 
radiating surface of any solid varies with the square of its 
lineal dimensions, while its cubic contents varies with the cube 
of the same. The cubic contents increases with linear size more 
rapidly than does the surface. Therefore, the smaller a body is, 
the more favorable is the ratio of its radiating surface to its 
cubic contents. The heat present in it from any cause varies 
with the cubic contents. Its output is proportional to the same, 
and the heat imparted to it varies with the output. 

A small transformer will cool more quickly than a large one, 
all other elements being equal. 

The tendency of electric engineering practice is to use special 
means for cooling transformers. 

OH Cooling. — Small converters are frequently oil-cooled. The 
converter is placed in a liquid-tight case, which is filled with 
oil. As the coil rises in temperature the oil becomes heated, and 
by circulating conveys the heat to the outside case. The air 
cools this, and thereby cooling the oil keeps down the temperature 
of the coil. The cut. Fig. 284, page 381, shows an oil-cooled trans- 
former with its coils lifted out of its case. This is a core-type 
transformer. In use the coils and cores are lowered into the 
case, and oil is poured in until it is full. Fig. 285, page 382, gives 
a separate view of the primary and secondary of the same type of 
transformer, with its coils surrounding the cores. 

Oil in a converter case performs another function, as it im- 
proves the insulation. 

A thermometer as shown in Fig. 288 is sometimes set into an 
oil-cooled transformer, in order to show how hot it is getting. 



TRANSFORMERS. 



385 



As the size increases, the heat imparted rises with the cube of 
the linear dimensions, and the superficial area rises only as the 
square. The cooling power is pretty closely proportional to the 
superficial area. Notwithstanding the wasteful heating of trans- 
formers, large-sized ones are exceedingly economical, often giv- 
ing over 98 per cent of return, a waste of less than 2 per cent. 

There would be no difficulty 
in making the transformer so 
large in proportion to its out- 
put that special cooling would 
not be required. But this 
would be so expensive that it 
would cost more than would 
the use of smaller artificially- 
cooled transformers. 

A characteristic feature of 
many transformers is the cor- 
rugated case. The shape is 
given to increase the area with 
which the air comes in contact. 

Water Cooling.— Water can- 
not be directly applied for 
cooling transformers, on ac- 
count of its effect on the in- 
sulation. It is applied indi- 
rectly by using a coil through 
which water circulates to cool 
the oil. The cut. Fig. 289, 
shows the interior parts of a 
shell-type transformer lifted 

out of the case. The core and coils are surmounted by a coil of 
pipe. In use the whole apparatus, core, coil, and water pipe, is 
immersed in oil in the transformer case. In the operation of 
the transformer, as the oil gets hot, the hotter oil rises to the 
surface. Here the hot oil would -naturally accumulate. The coil 
of pipe is immersed in this portion of the oil, and occupies the 
most effective place for cooling the oil. Water is kept circulating 
through it. 




Fig. 288.- 



-Thermometer in Trans- 
former. 



286 



ELECTRICIANS' HANDY BOOK. 



Air=Blast Cooling. — The cooling power of an air blast is often 
used for transformers. A current of air in rapid motion possesses 
far greater cooling power than when it is left to its natural cir- 
culation. The cut, Fig. 289a, shows an air-blast cooled trans- 
former. The air enters from below through a pipe communicat- 




FiG. 289.— Water-Cooled Oil-Filled 
Transformer Coils and Core. 



Fia. 289a.— Air-Blast Trans- 
former. 



ing with a fan or other source of air blast. The primary and 
secondary are wound in flat coils separated from each other by 
diaphragms. The core is so built up as to leave air ducts regular- 
ly spaced throughout. On the top there is a central damper to 
regulate the draft of air between the coils, and the damper on the 
side near the top regulates the draft through the core. At the 



TRANSFORMERS. 387 

bottom semicircular doors give access to the secondary terminal. 
The primary terminals enter on the top. 

The power required to operate the fan-blower is exceedingly 
small, about one-tenth of one per cent of the output. The fan is 
driven by an electric motor. 

Disk Winding. — Constructors of transformers often wind the 
low-tension coils disk fashion or concentrically, with one set 
of turns per layer, while its high-tension coils are wound out of 
wire of rectangular cross section. In the large transformers a 
number of wires are connected in parallel. This subdivision 
prevents in a great degree eddy currents in the conductors, just 
as lamination prevents it in the cores. 

The system used in the high-tension windings brings about 
another result. As one set of turns only is used for the width 
of each flat or disk coil, the electromotive force between neighbor- 
ing turns is never more than 25 volts, and sometimes is only 10 
volts. The principle is the familiar one used in the higii-tension 
winding of induction coils. It is called disk winding when 
applied to this class of apparatus. 

Ducts are arranged all through these coils, so that the oil with 
which they are charged starts into vigorous circulation at once 
when the heating due to service begins and no part of the iron 
is more than an inch distant from oil in motion. 

In larger sizes of transformers the cast-iron covers may simply 
be put in place without bolting down. A case could hardly 
arise in which a large transformer would be placed on its side. 
With small transformers, their covers are bolted on, so that 
they can be subjected to considerable jolting and inclined posi- 
tions without disturbance. 

Constant = Current Transformers. — A constant-current trans- 
former is one in which there is not a constant ratio of electro- 
motive forces between the terminals of the primary and second- 
ary coils, but in which a constant current is maintained by the 
secondary as long as a constant electromotive force is maintained 
at the terminals of the primary coil. This represents the require- 
ments of series lighting. 

An ordinary transformer gives on the secondary an almost 
constant virtual voltage and varying intensity of current. If 



tim 



388 



ELECTRICIANS' HANDY BOOK. 



the coils of the transformer be so constructed that the induct- 
ance of the primary and of the secondary portions are high com- 
pared with the mutual induction between them, the coil will give 
a constant virtual intensity of current to its secondary. One 
way of effecting this result is to have a choke coil in series with 
the primary coil. Special constructions of coils may be con- 
structed to answer the same end. A long core with the coils on 
the ends is one design. 

Electrical constructors have also devised transformers in which 
the result described above is produced by changing the distance) 
between the coils. 

The diagram. Fig. 290, illustrates the principle. C represents 







c 








i:.rfim 


s 
s 


mm 


s 

s 
p 


•.-•,-.-/.-".-."■•. 


p 


■ ;.:.-..-.;•:/: 













Fig. 293.— Action of Constant Current Transformbr= 

the iron core, P, P, the primary, and S, S, the secondary coil. 
The secondary coil is movable and suspended at the end of a 
lever with counterpoise, so that a little force will move the sec- 
ondary coil up and down. 

By Lenz's law (page 213), the induction of a current in the 
secondary coil will cause repulsion between the coils to be ex- 
erted. This varies in degree with the current induced. There- 
fore, in the apparatus any tendency to an increase of current in 
the secondary repels it from the primary, thereby diminishing 
the induced current. If the current grows less, the repulsion 
diminishes and the coils come nearer together, and the induc- 
tion is increased. 

The next cut, Fig. 291, shows the construction. In this the 



TRANSFORMERS. 



389 




fixed coil is seen at the bottom. The movable coil is suspended 
as shown above the fixed coil. It is held in equipoise by a lever, 
with counterweights. When a small current is taken from the 
secondary, the movable coil drops, and may even rest upon the 
fixed one. But as more current is taken from the fixed coil, the 
repulsion drives them apart, so as to dimin- 
ish the induced current. In this way a con- 
stant current is maintained with changing 
resistance on the outer circuit. The cut 
shows the sectional view of the transformer 
in the upper portion of it, with the 
plan below. If the resistance of the outer 
circuit supplied by the secondary coil is re- 
duced by the operation of arc lamps or by 
cutting one of them out of the line, the cur- 
rent increases momentarily, the repulsion 
drives the coils apart, the induced electromo- 
tive force falls in value, and the current 
through the new and less resistance under 
less electromotive force is unchanged. 

In larger transformers of this type there 
are two primaries, one at the top and the 
other at the bottom, both fixed in place, and 
two secondaries poised between them. With- 
out any output one rests against the upper, 
the other against the lower primary. 

One characteristic feature of this appar- 
atus is the counterpoising of one movable 
coil by the other one. 

An auxiliary lever is provided for adjust- 
ing the effects of attraction or repulsion between the coils. By 
adding or removing counterpoising weights, the adjustment is 
made. The apparatus shown has its coils immersed in an oil 
tank; the oil not only acts as a cooling agent, but damps the 
movements of the coils. 

Oil for Transformers. — The oil for filling transformers should 
be of low viscosity, so as to rapidly penetrate any interstice. 
High flashing point and high insulating value are also requisite. 




Fig, 291.— Constawt 
Current Trans- 

rORMEB. 



390 



ELECTRICIANS' KANDY BOOK. 



Sometimes sparking will make a little tube of carbonaceous mat* 
ter through oil which will constitute a permanent source ot 
trouble. 

Insulation in Transformers. — The most elaborate care has to 
be taken in insulating the windings of transformers. Tape, 
shellac, and mica are used. The laminations of the core or core 
plates are insulated from each other also in order to prevent 
Foucault currents. 

Direct Current from Alternating Current.— By special con 
nections to collecting rings on the shaft, an alternating current 
can be taken from an armature wound for direct current. The 

illustration. Fig. 292, shows a 
diagram of a Gramme ring 
wound for direct current. If 
rotated in a bipolar field with 
the connections shown in the 
cut, an alternating electromo- 
tive force will be impressed 
upon the circuit, if closed 
through the brushes and col- 
lecting rings. For the Gramme 
ring the general rule is that 
for single-phase current the 
connections must be taken from 
its windings at angular dis- 
tances equal to the pole spaces. For four poles there should be 
four connections, for six poles six, all evenly spaced, and con- 
nected alternately to one or the other collecting ring. 

In these windings, whether alternating currents are taken 
from them by means of connections to collecting rings, or wheth- 
er direct currents are taken from them by a commutator, the coils 
are subjected to precisely the same inductive influences, and 
identical electromotive forces are impressed upon the windings 
in both cases. 

Rotary Converter. — If an armature of a dynamo is provided 
with two sets of connections, one to a commutator for direct cur- 
rent and another to two, three, or four collecting rings for alter- 
nating current, a machine results which can receive one kind of 




Fig. 292.— Gramme Ring Giving 
Alternating Current. 



TRANSFORMERS. 



391 



current and act as a motor and deliver the other kind of current 
acting as a dynamo. Such a machine is called a rotary con- 
verter. The term continuous alternating transformer is applied 
to it in England. 

The machines can be driven by an alternating current as a 
synchronous motor, either for driving machinery or for generat- 
ing direct current, or for both. The latter current can be taken 
from the brushes bearing on the commutator. 

Use of the Rotary Transformer. — It is settled that for long- 
distance transmission of power the alternating current is to be 
preferred. It is in connection with such transmissions that the 
rotary converter is principally used. For many purposes direct 




Fig. 293.— Theory of Rotary Converter. 



current is preferable. Especially in high-voltage transmission 
is the rotary converter useful. 

Thus, a power station may generate electric energy, and trans- 
mit it any desired distance at a high voltage, so as to need only 
a small transmission line. It will in such cases practically 
always be of the alternating-current type. When it reaches a 
center of distribution, the current may go through step-down 
transformers, thereby giving an increase of current and diminu- 
tion of voltage. The current from the secondaries of the step- 
down transformers may be used to drive rotary converters, so as 
to produce direct current. Such an arrangement may be cited as 
particularly available for electric railroads on which direct- 
current motors are employed. 



892 



ELECTRICIANS' HANDY BOOK. 



Principles of Construction.— The diagram, Fig. 293, shows the 
principle of construction. An armature is indicated by its wind- 
ings, and is supposed to rotate in a magnetic field. The ends of 
the windings are connected to collecting rings and commutator 
segments. In the diagram each end of the winding connects to one 
of the collecting rings and then to one of the two commutator 
segments. Four brushes are provided; one pair for the direct 
current bear against the commutator, the other pair for the alter- 
nating current bear against the collecting rings. 

Alternating current received by the pair of brushes bearing 
against the collecting rings will cause the armature to turn 
when brought up to speed. It becomes a synchronous motor. 

Direct current can then be taken 
from the other pair of brushes, 
which bear against the commu- 
tator surface. In this case it op- 
erates as a converter of alter- 
nating into direct current. It 
may have its commutator 
brushes connected to a source 
of direct current. It then 
turns as a direct-current motor, 
and alternating current can be 
taken from the collecting-ring brushes. This latter use is com- 
paratively rare in engineering. The arrows in the diagram indi- 
cate the current relations. 

The next cut. Fig. 294, shows a drum armature with a regular 
commutator at one end of its shaft, and three collecting rings 
at the other. From each collecting ring a wire connects with 
the ^winding of the armature. The connections are 120° apart. 
One result is a three-phase current if the armature is rotated in 
a field by a direct current. The other result is a direct current 
if the machine is driven as a polyphase synchronous motor by a 
three-phase current. 

Relations of Voltage and Current. — The single-phase rotary 
converter operating to convert direct into alternating current im- 
presses a maximum voltage on the alternating-current circuit 
equal to that of the direct-current circuit. By the law of sines 




Fig. 294.— Drum Armature of 
Rotary Convebteb. 



TRANSFORMERS. 393 

the effective voltage on the alternating circuit is 0.707 of the 
direct-circuit voltage. If the rotary converter is operating to 
convert alternating into direct current, the direct-circuit voltage 
will be 1.41 times the effective alternating-circuit voltage. The 
effective current and the direct are in great degree the inverse 
of the proportion indicated above. All losses are neglected in the 
above general statement. Analogous ratios hold for polyphase 
rotary converters. 

The current in the armature of a rotary converter is made up 
of tv/o currents. One is that which passes through it. by the col- 
lecting ring brushes, the other is that which is induced by the 
poles, and which is delivered to the outer circuit by the armature 
brushes. The algebraic combination of these two constitutes the 
total, and as these two are generally opposite in sign, the actual 
current is small. This gives a small armature reaction and a 
small heating effect in the coils. 

Whether or not it is fair to call the distortion of the field of 
force by armature reaction the cause of the torque, there can be 
no electro-magnetic torque without such reaction and consequent 
distortion. The nature of the distortion determines the direction 
of torque, concentrating the lines of force under the leading 
horns of the pole pieces. 

The armature windings of the rotary converter, when it is per- 
forming its function of conversion of alternating into direct 
current, are traversed by a smaller current than when it is oper- 
ated as a direct-current dynamo. The output in power of which 
it is capable in its different roles, which is its working capacity, 
may be based upon the current it can carry with equal heating 
of the armature windings. The following power ratings are for a 
rotary converter used in the functions described: 



Continuous- 


Single- 


Three- 


Six- 


Current 


Phase 


Phase 


Phase 


Generator. 


Converter. 


Converter. 


Converter. 


1.00 


0.85 


1.34 - 


1.96 



Rotary Converter in the Three=Wire System.— The Edison 
three-wire system can be supplied by a rotary converter on the 
following system, applicable for a three-phase original current. 
The three secondaries of the step-down transformer on the high- 



394 ELECTRICIANS' HANDY BOOK. 

tension circuit are Y-connected (page 359). The free ends of the 
coils are connected to the three collecting rings of the rotary 
converter. The electromotive force between the junction of the 
coils, which is the natural point of the Y connection, and either 
of the armature brushes on the direct-current commutator is 
constant and equal to one-half of the electromotive force between 
the brushes. The neutral wire of the three-wire system may be 
connected to the neutral point of the Y, the other two wires to the 
direct-current brushes. 

Starting .a Rotary Converter. — If receiving power on the 
alternating side, the rotary converter has to be brought into syn- 
chronism. This can be very simply done by a small direct-current 
dynamo, which connected to the direct-current brushes will effect 
the result, when the alternating current can be substituted by 
way of the collector ring brushes. 

Functions of a Rotary Converter.— This machine can convert 
alternating current into direct current or the reverse. It can be 
used as a motor on either direct current or alternating current. 
It can be driven by power, and deliver either direct or alternating 
power or both at once. It may receive one kind of current and 
act as a motor, and generate the other kind of current simultan- 
eously. 

The Rectifier. — The alternating current rectifier is an appli- 
ance for converting an alternating current into a pulsating cur- 
rent of uniform direction, giving a series of half waves of identi- 
cal direction. Its use is principally for field excitation of alterna- 
tors. One or more of the armature coils is disconnected from 
the rest, and its ends are connected to the rectifier. The latter 
by its brushes delivers direct pulsating current to the field wind- 
ings, providing field excitation. 

The rectifier is a modification of commutator and collecting 
rings. It consists of a drum whose construction resembles that 
of a commutator. One bar or division is provided for each mag- 
net pole, giving an even number of bars. The bars are electrically 
connected in two sets, so that if they were numbered consecu- 
tively, the odd-numbered bars would be connected together, and 
the even ones also. Each set is insulated from the other set, and 
both from the shaft. The rectifier is mounted on the commuta- 



TRANSFORMERS. 



395 



tor shaft of the alternator. Each set of bars is connected to a 
terminal of the coil. There are two brushes, which are so ad- 
justed that one will be in contact with an even-numbered bar 
when the other is in contact with an odd-numbered bar; and if 
the two brushes are connected, then the alternating current from 
the armature follows this path. It goes to one brush, by a bar of 
one commutator set, passes through the wire of the outer circuit, 
including the magnet coil of the machine generally connecting 
the brushes, thence through the other brush and other set of 
commutator bars to the original coil. 

The entire current from an alternator may be passed through 
a rectifier. The alternating current from 
the armature of the machine is rectified, 
passes from one brush through its cir- 
cuit, including, it may be, lamps, field 
magnet of the alternator, and other 
things, and returns to the other brush 
of the rectifier. From the other end of 
the rectifier the original alternating cur- 
rent circulates through the armature. 

A rectified current may be used for di- 
rect-current operations, such as charging 
storage batteries, supplying direct cur- 
rent lamps, etc. It is not perfectly sat- 
isfactory for some uses, on account of 
its pulsatory character. 

A simple rectifying commutator is shown in the cut. Fig. 295. 
Two cylinders cut like crown gear wheels are nested together as 
shown, and are insulated from each other and rotate with the main 
shaft of the alternator. The heavy black lines indicate insula- 
tion. One is connected to one end of a wire from the armature 
coils; the other to the other end of the same wire. This wire 
may be an independent parallel winding, for the purpose of giv- 
ing current to excite the field. The brushes bear one on one 
tooth, the other on the next tooth of the commutator. Wires 
from the brushes go to the field, if it is to be excited, and connect 
in circuit with it. As the current in the wire from the armature 
changes in direction, the rotation of the commutator brings the 




Fig. 395.— Rectifier 
Commutator. 



396 ELECTRICIANS' HANDY BOOK. 

brushes to the other teeth. The effect is to send the rectified 
current through the outer circuit. 

An ordinary commutator can be used with its bars electrically 
connected into two sets of alternate bars, each set insulated from 
the other, provided it has one bar for each field-magnet pole. 

Operation of Transformers. — It has been impossible within 
the limits of the space at our disposal to go into full details of 
the theory of transformers. Owing to hysteresis and other factors 
the actual operation of a transformer is not so simple as the dis- 
cussion of it given here might make it appear. But the full 
treatment of the subject involves the application of the higher 
mathematics and is very intricate. The theory of the action is 
only given in outline and the statements are subject to qualifica- 
tion if the field of full investigation is entered on. 



CHAPTER XXIII. 

MANAGEMENT OF MOTORS AND DYNAMOS. 

Starting Motors. — The current must be given to a motor with 
some degree of slowness, or the armature may become overheated. 
After the motor is in rapid motion, the counter electromotive 
force protects the armature to an extent more or less consider- 
able. A stationary armature will be burnt out under conditions 
of voltage and current of the outer circuit, when it would be per- 
fectly safe if in its full rotation. 

The Starting Boxes.— Protection is given in their starting by 
the use of resistance. The resistance used is generally contained 
in a case with switch handle on its top and contact points. By 
swinging the handle frora point to point, resistances are cut out 
one by one until none are in circuit, and the motor receives as 
full voltage as is possible. The motor is started with all the 
resistances in circuit, and in series with the armature, and they 
are cut out as described until the motor is in full motion. Re- 
sistances cannot be economically used for running the motor. 

A simple construction is shown in Pig. 296. The switch is an 
arc of a circle shown in the middle of the cut. When turned 
clear to the right, the arc is out of contact with any of the four 
tongues. On turning it from the open circuit position, it first 
makes contact with contact No. 4, which is connected to the 
line. This contact is without effect. It next makes contact with 
No. 3. This sends the full current through the field. The next 
contact is No. 2. This sends current through the starting coil 
and armature, and the latter begins to rotate under the influence 
of the reduced current. Another contact remains, No. 1, which 
when made short-circuits the starting coil, and the armature 
receives the full working current. The long arc keeps all the con- 
tacts closed when in the last-described running position. 



398 



ELECTRICIANS' HANDY BOOK. 



Magnetic Release Starting Box.— A series of resistance coils 
are connected to a set of contact studs. An arm is arranged to 
swing on a pivot. In its motion its outer end moves over the row 
of studs, making contact with them one by one. Bach stud repre- 
sents a resistance held in a frame, which is back of the face of 
the apparatus. When the handle is swung to the left, as shown 

in Fig. 297, all the resist- 
ances are in series with each 
other. As the switch is 
moved to the right, it cuts 
out the resistances one by- 
one until none is left in cir- 
cuit. On the switch handle 
there is an armature of soft 




STARTING COIL 

UlAMMR 

FIELD COILS 

Fig. 296.— Simple Starting Box. 




Fig. 297.— Motor Starting Box 
WITH Magnetic Release. 



iron, which when the resistance is all cut out is brought by the 
motion of the switch arm directly in front of and against the 
poles of an electro-magnet. This magnet is secured to the face 
of the box, and is connected so as to receive part or all of the 
current received by the motor. 

A spring is arranged to pull the switch arm away from the 
magnet and across the face of the box to the position where the 



MANAGEMENT OF MOTORS AND DYNAMOS. 



399 



current is entirely cut out, where it strikes a stud and has its 
motion arrested. The attraction of the magnet for the armature 
is great enough to hold it against the pull of the spring. If the 
voltage of the circuit should increase, and thus produce an over- 
load, automatic cut-outs or fuses would presumably open the cir- 
cuit. The current would cease to excite the magnet, and the 
armature would no longer be attracted by it; the handle would 
fly off to the other end of its arc and come to rest with the motor 
circuit open. When the circuit breaker was replaced, new fuses 
put in, or in general terms when current was again turned on, 
the motor would be cut off and would only start by the regular 
process of moving the starting-box arm across the resistance 
contacts to the no-resistance running point. If the starting box 




Fig. 398.— Diagram of Starting-Box Connections. 



is not provided with the feature described, the current when 
turned on again would be apt to burn out the motor armature, 
unless some one had had the thoughtfulness to turn off the switch 
arm. Various constructions and arrangements are possible to 
carry out this principle. 

Starting=Box Connection. — The starting box is placed in series 
with the armature. The field if shunt-wound receives the full 
current which it is capable of passing; if compound-wound, the 
shunt winding receives its full current, the series winding re- 
ceives the current diminished by the starting-box resistances. 
These act upon the entire armature current, but only on part of 
the field current in compound-wound machines. In Fig. 298 B is 
the starting box, S is the shunt coil, and A is the armature of the 



400- ELECTRICIANS' HANDY BOOK. 

motor. The switch handle is horizontal when the motor is idle. 
It is turned clockwise. It connects the field first; then keeping 
this connected, current is passed through all the coils in series 
and the armature. Then the coils are cut out one by one as the 
handle is turned until the full current passes. 

Changing Voltage,— It is often desirable to transmit electric 
power at one voltage and transform it before use to another volt- 
age. For direct current this is done by a machine called a motor 
transformer, motor dynamo, or dynamotor. 

A Motor Transformer is a combined motor and generator. It 
has a single field magnet or set of field magnets, and a single 
armature is mounted in their field. The armature has two inde- 
pendent windings and a commutator for each winding; each 
commutator has its pair of brushes. Generally, the two com- 
mutators are placed at opposite ends of the armature. 

Action of the Motor Transformer. — The current from the 
original station passes through one of the armature windings and 
through the field coils. The terminals of the line are connected 
to one of the pairs of brushes. The machine, as far as this 
current and connection are concerned, is a motor, and its arma- 
ture rotates. As the armature rotates, it carries the other inde- 
pendent winding around, and electromotive force is impressed 
upon it. A circuit connected to its brushes has electromotive 
force impressed upon it, and if closed has a current induced. 

One of the independent windings is of a greater number of 
turns than those of the other winding. To decrease the electro- 
motive force, the winding of the greatest number of turns is used 
as the motor winding, and its brushes are connected to the actu- 
ating circuit. To increase the electromotive force, the winding 
of fewest turns is the motor winding. 

The relation of the original electromotive force to that im- 
pressed upon the second circuit by the generating coil is deter- 
mined by the relation of the turns in the one winding to those 
in the second winding. The cross-sectional area of the wires of 
the two windings is inversely proportional to the voltage ex- 
pended on the first coil and impressed on the first one. 

Step=Down and Step=Up Transformation.— A long fine wire of 
many turns in the first coil and a short thick wire of few turns 



MANAGEMENT OF MOTORS AND DYNAMOS. 401 

in the second coil give a diminution of voltage and an increase 
of possible amperage. This is a step-down transformer. A 
short thick wire of few turns in the first coil and a long thin 
one of many turns in the second coil has the reverse effect, and 
the combination is that of a step-up transformer. 

For the first coil the m.achine is a motor, for the second it is a 
dynamo. The first coil is the primary and the other the second- 
ary. In operation the primary coil passes a current actuated by 
the voltage from the station. Electromotive force is impressed 
upon the other coil, and any current up to the current-carrying 
capacity of the secondary wire, multiplied by the number of 
leads in parallel in it, may be taken from the brushes of what 
may be called the secondary commutator. 

riotor Transformer Practice.— Motor transformers may be dis- 
tributed all through a district. The current may be generated 
at a distant source, by water power for instance, and sent by 
several thousand volts potential through a small and conse- 
quently cheap wire circuit to any desired points in the district to 
be supplied. Or it may be sent to a single centrally-located trans- 
forming station in the heart of the district. Here it may actuate 
any number of motor transformers, and independent circuits can 
be taken off from each. These circuits radiating through the 
district will supply electric power most advantageously at low 
voltage. 

The Economy of flotor Transformers running at full load ex- 
ceeds 90 per cent. They are cheaply run as regards maintenance. 
The commutators need attention and ultimate replacement. New 
brushes have to be put on when the old ones are too far gone to 
yield to trimming, and adjustment. The great expense is the 
personal attendance required. A moving machine should not be 
left without someone to look after it. It needs attention some- 
times, even if it runs for hours without being touched. When 
attention is needed, it is apt to be rather urgent. A little neglect 
may lead to extensive injury. 

The expense of the labor item represented by the cost of the 
attendant workmen or engineers has operated to restrict the 
introduction of these machines. In Europe the system has been 
quite extensively employed. 



402 



ELECTRICIANS' BANDY BOOK, 



The other items of expense connected with it are estimated 
as considerably less than the interest and depreciation and 
energy loss charges in the direct-current low-potential distribu- 
tion from a distance. Where it is possible to concentrate the 
transforming under one roof in the heart of a district, the condi- 
tions are most favorable for its employment. 

Parallel Coupling of Dynamos. — Dynamos have to be coupled 
in parallel when the current to be sent out from a station ex- 
ceeds the capacity of one dynamo. When the current approaches 

the capacity of a single generator, 
if it seems probable that more cur- 
rent is to be required, a second 
dynamo must be connected in 
parallel with the other. It is. 
necessary also when the dynamo 
is to be replaced by another with- 
out interrupting the current. 

Parallel Coupling of Shunt 
Dynamos is shown in diagram in 
Fig. 299, in which the dynamos 
connected from bus-bar to bus-bar 
have their armatures indicated by 
Ai Ao, the shunt coils by Si S2, 
and the switches in th-e leads to 
the bus-bars by Bi Bo. To throw 
a dynamo in^ it is brought up by 
use of the field rheostat to a volt- 
age two or three volts over that 
of the system, its main switch B 
being open. When the voltage is attained, the main switch is 
closed. A voltmeter not shown in the cut is connected to the 
armature brushes or to the conductors near thereto. 

Parallel Coupling of Compound Dynamos.— The general con- 
nections are shown in the diagram, Fig. 300. A^ A, are the arma- 
tures. Si So the shunt coils, Fi F, the series coils, B, C, and D 
are the switches. P Q is the equalizer. They are supposed to be 
provided also with voltmeters, ammeters, and rheostats for their 
shunt coils. 




Fig. 399.— Shunt Dynamos in 
Parallels. 



MANAGEMENT OF MOTORS AND DYNAMOS. 



403 



The operation of starting a dynamo in parallel is thus con- 
ducted: The switch D is closed. The machine to be thrown 
into parallel is started and regulated by speed and field excitation 
until its potential is one or two volts lower than that of the 
machine already working. Then the switch B appertaining to 
the new machine, and which has hitherto been open, is closed. 

To throw out of action a machine running in parallel with 
another, the field excitation is reduced by the rheostat on the 
shunt coil until the load is only a few amperes. If this does not 
bring down the current enough, its speed of rotation may be re- 




FiG. 300,— Compound Dynamo in PAEALLEii. 



duced. Then the main switch B is opened and next the switch D 
on the equalizing wire. 

Trouble may follow from a machine accidentally stopping, as 
by a belt breaking. The machine thus freed of its load may take 
current from the other one, and begin to work as a motor. In 
each machine's circuit an underload circuit breaker should be 
included, which will break the circuit and prevent the motor 
action, 

Shuiit= Wound flachines in Series. — These dynamos are some- 
times connected in series. The only object of this connection is 



404 



ELECTRICIANS' HANDY BOOK. 



to increase potential. The current capacity of the two will be 
limited to that of the smaller one. Thus the two may have less 
current output than one. The potential is equal to the sum of 
the potentials of the two machines. 

Reversal of Direction of Armature Rotation.— The diagrams. 
Figs. 301 and 302, show how the connections of a dynamo must 
be reversed to change the direction of rotation of the armature of 
a series-wound machine. The diagrams represent a bipolar, 
shunt-wound dynamo. A and B are the field coils, and R is the 
regulating rheostat. The brushes are changed in position so as 
to give the reverse lead, and their connections are changed so 
as to connect them in the reverse sense with the two field coils. 





Figs. 301 and 302.— Reversal of Direction of Armature Rotation. 



This throws the rheostat out, so its connections have also to be 
reversed. The two cuts are self-explanatory. 

If the dynamo is separately excited, simply reversing the con- 
nections from the exciter will effect the requisite alteration of 
direction of armature rotation. This may be of special use in 
installations where polarity or direction of current is the critical 
point in operation. Such are storage-battery charging plants, 
electro-plating works, and direct-current arc lamp systems. In 
the latter the upper carbon must be the positive one. Otherwise, 
the greater portion of the light is radiated upward. 

Polarity Tests. — Blue litmus paper moistened and held against 
the positive wire gives a red color. Paper dipped in potassium- 
iodide solution gives a black color at the same pole. Paper 
dipped in a solution of starch containing a little potassium iodide 



MANAGEMENT OF MOTORS AND DYNAMOS. 



405 



dissolved in it gives a blue color. Other test apparatus and 
appliances are on the market. 

Alternators in Step, — In running alternators in parallel, 
not only has the potential to be kept the same for all the ma- 
chines, but the frequency of alternations or number of periods 
per second must be the same, and the machines must be in phase 
with each other. In throwing an extra machine into action in 
parallel with one or more running machines, all these three fac- 
tors have to be kept in view. The potential is brought up to the 
right point by changing the excitation of the field magnets; the 
frequency of alternations is brought to the proper point by 
changing the speed. 

Synchronizing. — Two transformers, T^, T2, Fig. 303, have their 




iH 




OMNIBUS BARS 



Fig. 303.— Synchronizing Alternators in PARALLKii. 



secondaries connected in series, one lead may include a voltmeter, 
the other an incandescent lamp, L. The primary of one of the 
transformers is connected to the terminals of one machine or else 
directly across the bus-bars; the primary of the other is con- 
nected to the terminals of the machine which is to be thrown 
into action. If the new machine, B, is operating in synchronism 
with the system or with machine A, the two transformers will 
co-operate in lighting the lamp. As the new machine is started, 
the lamps are lighted by the combined effect of the two ma- 
chines. The new machine is speeded up by turning on power, 
and as the frequency of the machines approaches equality, the 



406 E'LEGTBIGIANS' HANbY BOOK. 

light of the lamp begins to vary in brightness. At first the 
variations are very quick in following each other. As the hith- 
erto idle dynamo is speeded up, the frequency of its phases 
increases and approaches closer to that of the other machine. 
The lamps now vary more slowly, rising and falling regularly. 
The rising and falling grows slower and slower until a point is 
reached where it ceases and the lamps burn steadily. Meanwhile 
the voltage must have been kept right by adjusting the excitation 
of dynamo B. The voltmeter, not shown in the diagram, is used 
to direct this. At the instant when the lamp burns steadily 
the switches S2 are closed, throwing the machine into the work- 
ing circuit. Its voltage must be as nearly as possible that of the 
circuit when the switch is closed. 

The parallel working of alternators is made possible by the 
following fact: When running in phase with each other, alterna- 
tors tend to preserve their phase relation, or to run in synchron- 
ism. If one has a tendency to change its synchronism, reaction 
with the other pulls it up. 

Regulators or Boosters.— The potential given by a primary or 
secondary battery is increased by placing extra cells in series. 
In the secondary battery these are called end cells. If a dynamo 
gives insufficient voltage, an extra dynamo may be placed in 
series with it to add to the voltage. The second dynamo is 
called a regulator, compensator, and less elegantly but far more 
frequently, a booster. 

The ways of arranging booster circuits either with or without 
storage battery are numerous, and are subjects of a number of 
patents. 

Booster Connections.— A very usual method of connection is to 
place smaller dynamos as boosters upon the various feeders as 
required. The principal current is supplied by one or more 
dynamos running at constant voltage, which is the minimum 
required. From this dynamo the lines run directly to the bus- 
bars. From one bus-bar the feeders are led directly to the dis- 
trict. From the other bus-bar leads run to one set of terminals 
of smaller dynamos, and the other terminals of these dynamos 
are connected to the other leads of the feeders. The smaller 
dynamos are the boosters. 



MANAGEMENT OF MOTORS AND DYNAMOS. 



407 



Tlie cut, Fig. 304, shows a typical arrangement. The principal 
Qynamo is shown at D, and B and B are the feeder dynamos or 
boosters. The armatures of the dynamos B and B may be in 
series each with its own feeder. In such case the fields are sepa- 
rately excited. Often current is taken from the main dynamo 
for this purpose. On varying this current by a rheostat, the 
intensity of field and consequent electromotive force given by 
the boosters are made to vary. The main generator has to pro- 
duce the full current and more than one hundred (two-wire sys- 
tem) or two hundred (three-wire system) volts electromotive 
force; the boosters have to pass only a fraction each of the full 




Ftg. 304.— Boosters. 



current, and impress a few volts electromotive force on the cir- 
cuit. Their armature resistance may be quite low. 

Hand Regulation of Booster. — The boosters have to be regu- 
lated so as to add more or less potential to that of the system 
in accordance with the R I drop. The field of the boosters may 
he excited by independent dynamos, and the field current in the 
boosters can he increased or diminished by rheostats or other 
appliances. Thus a rheostat may be placed in series with the 
field of the booster, and may be used to let more or less current 
flow through its coils, or the exciting dynamo may be regulated 
by its own field rheostat so as to give more or less current to 
the booster's fields. The operative has to shift the rheostat 
handle from time to time or otherwise modify the field excitation 



408 ELECTRICIANS' HANDY BOOK. 

of the booster to suit the requirements of the supply for the 
district. 

To carry out the hand regulating system, the armature of the 
booster is connected in series with the feeder line which it regu- 
lates. The feeder is connected directly to the brushes, and the 
armature in its separately-excited field is driven by the engine. 

Automatic Regulation of Boosters. — The regulation of the po- 
tential added to the circuit by boosters can be made automatic 
as well as very accurate by vv^inding their fields and armatures in 
series with each other and connecting them in the feeder circuit. 
The feeder current goes through both field and armature. As 
the current increases, the series-wound booster responds, because 
of the increased current in its field. Its field excitation grows 
with the current, and a higher potential is developed. As cur- 
rent is diminished less goes through the field-magnet windings of 
the boosters, and they give a lower voltage. 

By modifying the field windings of the boosters, all sorts of 
effects can be secured, some analogous to those due to over- 
compounding. The feeders in the district connect with mains, 
and these with leads. As current increases, the drop on the 
feeders is not all that is decreased. The mains and leads also 
feel the loss in potential. The boosters can be so proportioned as 
to give some volts more than those of the drop on their respective 
feeders, so as to take care of the mains and leads also. If the 
drops on the feeder at maximum load were three volts, there 
might be one or two volts additional drop beyond the point of 
attachment of the feeder among the leads of the system. It 
is often advisable to give more potential increase within the 
feeder than its own drop, to compensate for the drop beyond it. 
It is a sort of over-compensating. This may apply to any feeder- 
system. 

Booster Construction. — The booster to act as described needs 
a high range of adaptability and power of varying its field 
strength. It may be said to require flexibility of action. The 
main point is to give it large field cores, so that the iron of the 
cores will never approach saturation, or else to have fewer turns 
than usual in the field coil. 

riotor Dynamos as Boosters,— The current from a dynamo 



MANAGEMENT OF MOTORS AND DYNAMOS. 



409 



may be used to actuate a motor dynamo, and the current from 
the generating coils of the latter may be used as a booster cur- 
rent. The motor dynamo is practically a dynamo driven by an 
electric motor. The current from the station dynamo would 
pass through the motor to the feeders and mains of the system. 
The subsidiary dynamo driven by the motor would be connected 
to the feeders. As the line drew upon the station dynamo for 
more current, the motor would turn faster, because more cur- 
rent would go through its coils. This would cause the subsi- 
diary dynamo to rotate faster and to impress more electromotive 
force upon the system. This system would contain the automatic 
regulating feature. 

Nowhere in the field of electric engineering does the inter- 



Mil I 
I I I 



Fig. 305.— Equalizing Dynamos in ihree-Wire System. 



changeability of dynamo and motor appear more clearly than in 
the uses of dynamos now being described. Their application to 
regulating lighting circuits is comparable to that of storage bat- 
teries, such application being based on the double role which such 
machines can play, at one time taking power from the system and 
acting as motors, at another time giving power to the system and 
acting as dynamos. 

Compensators.— This word has been used as a synonym for 
boosters. When a purely compensating action, and not a dis- 
tinctively intensifying action, is performed, it is specially appro- 
priate. The diagram. Fig. 305, shows the use of compensators 
on a three-wire system. The compensators B C are shunt-wound 
dynamos, coupled together mechanically, so that they rotate at 
the same speed. They are connected across the system, each 
dynamo being between the neutral and an outside wire. 



410 



ELECTRICIANS' HANDY BOOK. 



In parallel with them, and between them and the main dynamo 
A, a resistance F G is placed across the outside leads. The 
neutral wire does not extend back of the compensators; it runs 
from between them out to the system of distribution; there are 
only two leads from the main generating system. 

The resistance is so arranged that but a slight current flows 
through the dynamos when the two leads are equally loaded. 
If by extinguishment of lamps or other appliances the wires re- 
ceive unequal current, the compensator connected to the wire 
carrying the lighter current acts as a motor. Turning under the 
influence of the current, it drives the other dynamo and gener- 
ates current for the other more heavily loaded line. 

Floating Battery. — Boosters are often operated in conjunc- 




B 
Fig. 306.— Floating Battery. 

tion with storage batteries. A storage battery connected across 
the two or three leads of a system, as shown in Fig. 306, is 
termed a "floating battery." It works automatically. When the 
voltage of the system tends to rise because of small consumption 
of current, the battery receives current and is charged from the 
main dynamos. When the district needs a heavy current, the 
battery discharges into the leads and assists the dynamos. 

This arrangement is the simplest, and is supposed to work 
automatically. An auxiliary dynamo or booster is generally 
used to assist the regulation. It acts to raise and lower the 
voltage of the system. 

Booster and Storage Battery Connections are shown in 
Figs. 307, 308, and 309. In Fig. 307 G is the station dynamo, B 
is a series-wound booster, S indicating its series coil; E is the 
storage battery and MM indicate motors in the district. At 
normal load the generator supplies just the right current, the 
voltage of the battery is equal to and opposed to that of the line, 



MANAGEMENT OF MOTORS AND DYNAMOS. 



411 



and no current goes through the field S of the booster, and the 
booster voltage is zero. When the load increases and more cur- 
rent is taken from the station dynamo G, the voltage of the sys- 
tem falls a little, the battery begins tp discharge through the 
field S of the booster, and the latter adds electromotive force to 
the system. If all is in proper proportion, the electromotive 
force added will be just enough to compensate for the drop due 
to the loss of potential of the main generator. The battery dis- 
charges through field and armature of the booster, and the latter 




-=:r-E 



Fig. 307.— Booster and Storage Battery Connection. 



having its field excited with current with the polarity due to the 
battery's discharge, adds its voltage to that of the battery. 

If the voltage in the outer circuit due to the generator rises, 
this holds back the battery current and the booster field becomes 
inactive, and the booster ceases to generate current. As the 
voltage in the outer circuit rises still further, it exceeds that of 
the storage battery, and a charging current flows. This "ener- 
gizes," as it is called, the field of the booster, but with opposite 
polarity to the original, so that now it acts to help charge the 
battery. 

The whole arrangement works like a floating battery. The 
booster reinforces the action of the battery. It may be termed a 



412 



ELECTRICIANS' HANDY BOOK. 



floating booster. The system can only be used where voltage 
falls with load increase. 

In Fig. 308 a compound-wound booster B is supposed to be 




Fig. 308.— Booster and Storage Battery Connection. 

employed and is connected as shown. At normal load the excita- 
tion of the series field S is equal to that of the shunt field +. 
These two field coils are oppositely wound, so that they counter- 




FiG. 308. -Storage Battery* and Booster connection. 



act each other under this condition, and the booster generates 
no current. If the external load is increased by more power 
being taken in the district, the series field coil S of the booster 
receives more current than the shunt coil, and the preponder- 






MANAGEMENT OF MOTORS AND DYNAMOS. 413 

ance excites the booster, so as to cause it to generate current in 
direction the same as that of the battery current. The booster 
and battery now add to the voltage of the line. 

If the external load decreases, the series coil gets less current 
than the oppositely-wound shunt coil. The polarity of the field 
of the booster is thus the reverse of what it was. The booster 
sends current into the battery and charges it. 

In the two last arrangements the booster and storage battery 
are in series with each other. The next cut, Fig. 309, shows a 
booster B with shunt field coil f and series field coil S, opposed to 
each other in winding, but with the storage battery in parallel 
with generator and motors, while the booster is on one of the 
leads between battery and generator. The booster voltage is 
added directly to the generator voltage. At normal load the 
magnetization of the shunt coil f exceeds that of the series coil 
S, and the electromotive force of the booster is of the same polar- 
ity as that of the generator, so that it reinforces the current 
due to the generator. The battery is of such number of couples 
that its normal voltage is equal to that of the sum of the genera- 
tor and booster voltages. If an excess load comes on the system, 
more current flows through the line, and consequently through 
the series coil S. This coil works against the shunt coil f. 
Therefore the voltage of the booster is diminished, and the bat- 
tery discharges on the line and takes up its share of the work. 
On decrease of load the field due to f preponderates, and the 
booster increases the voltage on the line until at low enough 
load this voltage exceeds that of the battery, and the battery 
receives a charge. 

Crushers. — This term is sometimes applied to a motor used to 
reduce the potential on a feeder line. Assume that there are 
several feeders running out from a station, and that some re- 
quire higher potential than others. The main dynamo can be 
run so as to give a higher electromotive force than that required 
by some feeders. On such feeder lines a motor would be placed 
which would absorb the extra voltage. The main generator's 
voltage would be lower than that required by other feeders, and 
on these feeders boosters would be placed, which in whole or in 
part would be driven by the motor. The latter would be a 



414 



ELECTRICIANS' HANDY BOOK. 



80 VOLT 
ARMATURE 



120 VOLT 
ARMATURE 



40 VOLT 
ARMATURE 




"crusher." The term is inelegant, and something better should 
be found for it. The same is to be said for booster. Abbott 
applies the term compensator so as to include all such appli- 
ances. 

The Crocker=Wheeler System of Speed Control is especially 
designed for use in machine shops. It utilizes three dynamos, 
A, B, and C, Fig. 310, connected in series and with the three arma- 
tures on one shaft. The three armatures are practically con- 
nected in series across the circuit. 

Suppose the circuit to have a potential difference of 240 volts. 

Then the three armatures 
are wound for 40, 120, and 
80 volts respectively. Four 
leads are taken from the ma- 
chines. One is at one end, 
another at the other end, 
and two intermediate ones 
are taken from between the 
machines. These leads are 
carried through the shop 
Wiiere power is to be uti- 
lized. The speed of the 
motors driven is regulated 
by changing the voltage ab- 
sorbed by them. A two- 
wire power lead of definite 
voltage is by the rotary 
transformers converted into a four-wire system. 

It will be noticed that the machines vary in voltage, and that 
the machine of highest voltage is placed between the others. 
The object of this will be seen. If a machine is to be run slowly, 
its terminals are connected across the 40-volt leads. The next 
degree is the 80-volt, and then the 120-volt lead. Each of these 
voltages can be taken off a single machine. Next the 40-volt and 
120-volt machines can be put in series, giving 160 volts, then the 
120 and 80 volts, giving 200 volts, and finally all three machines 
in series, giving 240 volts. 
This gives six voltages. The tool to be driven is provided with 



Fig. 310.— CROCEBR."WHEETi^R MULTIPLE 

Voltage Speed Control. 



MANAGEMENT OF MOTORS AND DYNAMOS. 415 

its own motor, controller, and resistance coil. The six voltages 
give six speeds. Each voltage can be modified in its action by 
the resistance coil. Thus twelve speeds are obtained by a single 
resistance coil added to the four-wire system. 

Any motor can be caused to vary in speed within certain limits 
by the use of a rheostat, which changes the current received by 
it. A motor with the rheostat control superadded to the multiple 
voltage control can b-e made to vary in speed by so many degrees 
of change as to work almost by insensible gradations. The rheo- 
stat takes the place of the resistance coil spoken of above. 

Accidents to Motors. — There are two principal causes of acci- 
dents. One is the burning out of the armature. This is guarded 
against by giving current slowly, by the us-e of a rheoctat or 
starting box. The other is destruction of the armature windings 
by too high speed. A run-away motor may have the binding 
v/ires on the armature break by centrifugal force acting on the 
windings. The latter are then driven against the pole faces, 
wrecking the machine. Too high speed should be guarded against 



I 



CHAPTER XXIV. 

CARE OP DYNAMOS AND MOTORS. 

Reversing the Direction of Current in a direct-current dy- 
namo or of motion in the same type of motor is effected by revers- 
ing the armature connections. This reverses the polarity of the 
core, and causes it to be subject to torque in the reverse direc- 
tion. If metal brushes or considerably inclined carbon brushes 
are used, their direction of inclination or "rake" should be re- 
versed, to prevent the ends from catching on the commutator. 
Radial or even steeply-inclined carbon brushes need not be 
reversed. In multipolar machines the connections are shifted 
an angular distance equal to that intervening between the poles. 
The easiest way is often to simply rotate the brush yoke through 
the arc of this number of degrees, carrying all the brushes 
with it. Sometimes such reversal cannot be allowed, as it in- 
terferes with regulating apparatus. Changing the main connec- 
tions reverses the polarity of both field and armature, and leaves 
the direction of revolution unchanged. 

Stopping a riachine.— When a machine is being stopped, the 
brushes should be kept on the commutator until it is running 
rather slowly. Then they are lifted off the surface. The object 
is to remove any chance of injury from a possible reverse move- 
ment of the armature. Strictly radial carbon brushes are almost 
free from danger in this regard. 

Too High Speed. — This is a cause of trouble. It may involve 
a strengthening of the field, so as to doubly raise the electro- 
motive force and cause sparking, which is to be cured by weak- 
ening the field. But too weak a field is in itself a cause of 
sparking. A field regulator may be used to adjust the strength 
of field. If so, it is a good precaution to use one without any 
zero point, or "infinite resistance," especially in the case of 

416 



CARE OF DYNAMOS AND MOTORS. ill 

motors. A motor without load and with current passing through 
the armature and the field cut out, will infallibly wreck itself 
by racing. 

Loss of Magnetic Polarity. — A field magnet may lose its 
polarify. This may be due to long standing, so that the residual 
magnetism is lost, and the machine refuses to build up. It may 
also be due to wrong polarization of the field by means of a cur- 
rent of wrong direction. Such a current may be produced when 
so intense a current passes through an armature with advanced 
brushes that the armature reaction changes the polarity of the 
field. This may be due, in a shunt-wound machine, to a short 
circuit in the field. This wrong direction of current in the magnet 
coils is especially to be feared in compound-wound machines. 
Its results are especially bad in storage-battery work. Reversal 
of the magnetization of a field when the machine is charging a 
battery converts it into a motor, and the current from the battery 
drives it. Thus the battery loses any charge which may have 
been given it. The battery as it becomes more highly charged in 
regular working may be the agent in reversing the polarity of 
the field. 

Wrong Polarity of Field.— Sometimes it happens that the 
winding of a machine is such as to give the wrong polarity to 
the pole pieces of the field. This happens especially with mended 
machines. One thing to do is to recall the law of polarity, page 
210, and to try to follow it out in the connections. Another is to 
try reversing the magnet connections. There should be no diffi- 
culty in arranging the connections so as to alternate north and 
south poles all around the field. The thing to remember is that 
in settling whether the current runs with or against the clock, 
the observer must conceive himself as facing the hollow in the 
pole piece which embraces the armature. 

The brushes are raised from the commutator, and a current 
of proper direction is sent through the shunt winding for a few 
seconds. The machine can then be started again. 

Refusal of Motor to Start. — Connect an incandescent lamp 
or voltmeter between one of the leads and one of the binding 
'posts of the motor. The lamp is the best, as it operates to some 
extent as a current tester as well as potential tester. If the lamp 



418 ELECTRICIAN^ 8' HANDY BOOK. 

on one side shows no light, try a connection across from binding 
post to binding post, and then if the lamp lights, current passes, 
and the trouble is in the motor. If the line shows no current, a 
safety fuse is probably blown out or loosened. See if the brushes 
touch the commutator. If the line and motor seem to be all right, 
shift the brushes back and forth in search of the working point. 
If the motor will not go, it probably has too great a load. If a 
shunt motor is too heavily loaded, the armature refusing to 
start, develops no counter electromotive force, and practically 
short-circuits the field so as to impair the magnetization of the 
field. 

When a motor 'vill not start, and the connections seem to be all 
in order, the current should be cut off, and the clutch opened, or 
belt thrown off, so as to take the load off the machine. The arma- 
ture must then be set in motion by hand, and the current turned 
on while the armature is turning. Do not turn on the current 
while the hand is touching armature pulley or delt. When the 
machine is rotating regularly, throw on the load gradually. Re- 
member that a motor which refuses to start is in great danger of 
burning out its armature windings if the full current is left on 
for any appreciable time. The field coils also may suffer from 
overheating. This is another reason for starting slowly. Give 
current very slowly, and never anything like full current if the 
motor does not start. 

Slow Speed Without Load indicates in a motor an insufficient 
field magnetizing current or that the connections are inverted. 

Idle Motors.— When a motor is doing no work the current 
should be cut off. A motor running without load consumes cur- 
rent, and this if a meter is used, has to be paid for. 

Speed Regulation of Motor Without Load.— On suddenly 
throwing the load off a series-wound electric motor, as by shifting 
a belt or loosening a clutch, its speed will be suddenly and perhaps 
dangerously increased. The rheostat or starting box should be 
manipulated so as to prevent this sudden increase of speed. A 
shunt-wound motor does not act thus, and does not need the 
above precaution. 

Starting and Stopping flotors. — These operations should be' 
performed gradually. A sudden throwing on or off of a load on 



CARE OF DYNAMOS AND MOTORS. 419 

a motor affects the circuit soraetimes to quite remote points. 
Large motors should for this reason alone be started and stopped 
slowly. In sudden, jerky starting there is also involved a great 
waste of power. Such wasteful manipulation is often very notice- 
able on trolley cars. The duty of the superintendent of power 
plants is to prevent all sudden starting and stopping of motors as 
far as he possibly can. 

Bad Contacts Between Winding and Commutator Bars. — The 
wires of the armature windings in some machines, especially 
those of earlier date, are connected to the commutator bars by 
means of screws. If a screw gets loose, resistance is introduced 
with danger of sparking, which will occur between the brushes 
and the badly-connected commutator bar. Thus, on stopping the 
machine the defective place can be located by the appearance of 
the bar. Properly-soldered connections in modern machines 
rarely fail, unless too many wires are bunched into one soldered 
joint. 

Temperature of Commutator. — The commutator should not 
rise to a temperature exceeding 185° F. (85° C.) 

A usual cause of heating of the commutator is too great pres- 
sure of the brushes against its surface. Relieving this pressure 
by weakening the action of the springs will contribute materially 
to the duration of both commutator and brushes. 

Collector Rings on alternators and alternating-current motors 
must be kept bright and clean. A little vaseline can be applied 
from time to time. If the surface is rough, the machine must be 
stopped, the brushes lifted off, the armature or rotor started 
turning again, and the rings may be sandpapered. Use a hollowed 
block of wood to hold the sandpaper. 

Materials of Commutator. — To withstand the action of carbon 
brushes, the commutator bars are made of hard copper (unan- 
nealed). But however hard the copper may be, it is apt to be 
more subject to wear than is the mica insulation which lies 
between the bars. Too hard or unwearable mica tends to project 
beyond the copper after a machine has run some time, and thus 
impairs the commutator surface. The projecting mica tends to 
cause the blushes to jump up as it passes, and occasions the worst 
kind of sparks, with lots of "extra current" behind them. Com- 



420 ELECTRICIANS' HANDY BOOK. 

mon sandpaper is often not able to cut down the ridges. If not 
afraid of injury, emery or carborundum cloth or paper may be 
tried. The worst of this trouble is that it is slow to .reveal itself. 

Loose Commutator Bars. — ^Sometimes these are a source of 
trouble. By holding a somewhat wedge-shaped piece of wood 
on each bar and striking it with a hammer, looseness can be de- 
tected. The internal insulation of the armature or the rings 
holding the commutator together may be in fault. The cure is 
to be intrusted to a competent person only. It may differ for 
different cases to an indefinite extent. 

Oval Commutator. — Especially if made of cast metals, commu- 
tators sometimes wear irregularly and become oval in cross sec- 
tion. The only cure is to turn them down in a lathe. 

A Qummy or Sticky Commutator Surface will cause the 
brushes to chatter or execute a series of little jumps. Cleaning 
is the remedy, with a very little oil. Do not attempt to stop it by 
lubrication, as this will make resistance at the contact of brush 
with commutator. 

Lubricating tlie Commutator Surface. — Sparking often fol- 
lows as a result of this practice. If the surface is in good order 
and the brushes are properly shaped and trimmed, hardly any 
lubrication should be required. Electric contact of the best 
quality is required between the brushes and the commutator 
surface. Anything in the nature of grease acts as an insulator. 
A drop or two of oil carefully rubbed over the whole surface 
should be sufficient lubrication. 

Brushes and Brush Holders.— These should not be so heavy 
that they will not readily yield to the inevitable inequalities of the 
commutator surface. The width should range from % inch to 
11^ inch. The thickness prescribed by the manufacturer of the 
machine should be adhered to. For holders drawn copper is one 
of the best materials. Cast-metal holders are not generally 
recommended. 

Brush Pressure, —A carbon brush may press with a weight of 
2 to 2^4 pounds on the commutator; a copper brush should not 
press much over a pound. Good contact between carbon brushes 
and brush holders must be secured. For this object carbon 
brushes are copper-plated. 



CARE OF DYNAMOS AND MOTORS. 421 

Replacing Brushes.^In putting new brushes in place, the 
surface resting on the commutator should be made to fit accurate- 
ly. A simple way of shaping them is to hold a sheet of sand- 
paper, rough side out, on the surface of the commutator, and 
to rub the bottom of the brush back and forth thereon, the brush 
being held firmly in the brush holder. If the machine shows any 
inclination to spark with a new brush, it is well to run it without 
load for a while until the brush shapes itself. 

Position of Brushes. — Opposite brushes should be placed so as 
to bear upon different portions of the commutator surface. If 
in the same plane at right angles to the shaft of the machine, they 
will wear a groove in the commutator. As far as possible, the 
entire surface of the commutator should be rubbed by the brushes. 

Copper Brushes must be cut square at their lower end ; especial- 
ly is this to be done for wire gauze brushes. They should be 
pressed just enough and not too much against the commutator. 
They should not vibrate when the armature is turning. Once a 
week they should be washed with benzine to remove grease and 
oil, and should be put in service again only when perfectly dry. 

Carbon Brushes are of lower conductivity than copper brushes. 
More carbon brushes are required for a given machine than 
copper brushes, which exacts a longer commutator. There must 
be no lost motion in brush holders or yoke. The screws and other 
movable parts of these portions of the machine must be watched. 
If anything is loosened, it must be repaired or tightened. 

Setting Brushes. — In putting in the brushes, they must come 
in contact with the properly-spaced commutator bars. The gen- 
eral rule is to divide the number of commutator bars by the num- 
ber of poles, and set the brushes that number of bars apart. An- 
other way to get at their position is to lay a strip of paper around 
the commutator and cut it to exactly the circumference thereof. 
This can be divided with dividers accurately into as many equal 
parts as there are poles in the machine, and the divisions marked 
with a pencil. A simpler way is to do it by folding the paper. 
By placing it again around the commutator the pencil marks or 
the folds will show how to space the brushes. This applies espe- 
cially to setting tangential metal brushes. Direct-bearing carbon 
brushes tend to find their own place. 



422 ELECTRICIANS' HANDY BOOK. 

It metal brushes are used, the greatest care should be exercised 
to avoid the commutator turning in the wrong direction, as this 
bends up their ends, and may injure or short-circuit the commu- 
tator bars. 

The difficulty in setting brushes arises from the fact that differ- 
ent machines require different setting. Once set wrong, enough 
sparking may occur to so deteriorate the commutator that spark- 
less adjustment will be impossible. Another source of damage 
may be the simple heating of the commutator on account of 
wrongly-set brushes. 

There is no rule to be given for setting brushes. For each 
type of machine it must be learned. The information can be 
obtained from the manufacturer if it is a new machine, or from 
the engineer who ran it if it is an old one. 

In the old two-pole machines it was a general rule that the 
brushes should be 180° apart. In more recent two-pole machines 
the angle between the brushes is often little more than the angle 
subtended by one of the pole pieces. On such machines a mark 
is generally made for the brushes to be set by. The older ma- 
chines had two marks, one for load, the other for no load. The 
general rule is to shift the brushes in the direction of the rota- 
tion, as a dynamo receives its load, and vice versa for a motor. 

Hard Carbon Brushes have sometimes to be rejected. One 
may be what some engineers call "glass hard," often harder than 
glass, or may be of high resistance. Such must be rejected and 
replaced by good ones. They cannot be made to work satis- 
factorily with brushes of the proper degree of hardness. 

Lifting Brushes. — When a machine is in operation generating 
current, a brush should never be lifted from the commutator. 
If there are several brushes on the same side, a single one may 
be lifted, but the best practice is not to do so. If there is only 
one brush and it is lifted, it may make an arc and burn the com- 
mutator. 

A good way to test the heating of the armature is to hold the 
hand in the draft of air coming from it. If the armature is hot, 
the air will be heated. 

Break in the Armature Windings. — This accident causes a 
motor to spark very badly and may increase its' speed. On stop-. 



CARE OF DYNAMOS AND MOTORS. 423 

ping it, the insulation between the commutator bars between 
which the broken coil is connected will show the effects of the 
sparking. If a dynamo refuses to build up, and this trouble is 
suspected, the machine can be run as a motor so as to identify 
and locate the place by burning the insulation as just described. 
If there are a great many commutator bars, the two involved 
can be temporarily connected by solder, so as to short-circuit the 
defective coil. The real remedy is to connect the ends of the 
broken wire with silver solder. A break will sometimes only 
show itself when the machine is running, when it will produce 
flashing between the commutator and brushes. When motionless, 
the severed ends may spring together. By determining the exact 
resistance of the armature the trouble may be found, as the break 
will probably increase the resistance if it does not absolutely 
break the circuit. A short circuit may exist under like condi- 
tions. 

If a commutator gets too hot, it will heat carbon brushes and 
get a coating from them, which will increase its superficial re- 
sistance and aggravate the trouble. The commutator blackens, 
and the carbon holders get hot and may become discolored. Such 
heating should not occur. 

End Motion in an Armature Shaft is generally desirable. 
With the usual cylindrical commutator this motion causes the 
brushes to come in contact with the entire surface of the commu- 
tator if the range of motion is sufficient, and such contact favoj-s 
even wearing, and the cylindrical contour of the armature is 
thus favored. If the armature shaft has end play, the belts are 
pretty sure to have irregularity enough to keep it in constant 
motion back and forth. 

In some machines, end motion is given by mechanism for the 
purpose. 

Short Circuits In Armature. — The windings may get their 
insulation rubbed off and connect with each other or with the 
iron core of the armature. Copper or carbon dust may be the 
cause of short circuits between commutator bars. A commutator 
brush may be in electric contact with the frame of the machine. 

If a machine were perfectly insulated from the earth, such a 
single contact with core or frame would be without any effect. 



424 ELECTRICIANS' HANDY BOOK. 

If the frame of a machine is grounded and a ground exists in the 
commutator or armature, then such a contact of winding and arm- 
ature core causes a short circuit, which may burn out the arma- 
ture windings. When any short circuit of this character exists 
it is a menace, although it may do no harm for a long time. The 
short circuit can be sought for with a galvanometer and a source 
of current, such as a dry battery. The armature windings are 
disconnected from the field windings, and one end of the wire 
from the galvanometer and battery is kept in contact with the 
iron core of the armature or with the frame of the machine. With 
the other end of the wire the armature bars, brush connections, 
etc., are touched. A movement of the galvanometer needle indi- 
cates the contact and locates it. It is obvious that the magnet 
windings may be tested also by touching the exploring wire to 
their ends, as contact may exist between magnet core and magnet 
windings. Repairs have generally to be made at the factory. 

Frequently a battery with wires is sufficient to detect these 
troubles. A spark will show when contact is broken, or the 
tongue may be placed betM^een the wires, and the taste will reveal 
a leakage. 

A single contact between the armature winding and the iron 
core of the armature does no harm as long as no other contact or 
grounds exist. Of course, it should not be tolerated, as it is a 
constant menace. A short circuit due to the contact of two wires 
of the same coil of the armature winding may have serious con- 
sequences. A dynamo with this trouble will not build up or 
excite itself. If the attem_pt is made to start it with an outside 
source of current, it will not absorb its full voltage, and the arma- 
ture windings will begin to get hot. This will be indicated by 
the smell of heated insulating materials. On stopping the ma- 
chine, the defective coils can be found by feeling the surface of 
the windings. The hottest part will be where the short circuit 
is. A motor will show such a short circuit by loss of power and 
speed. Sometimes it will not move at all. Entire or partial 
rewinding of the armature is the cure. 

If the short circuit is between two wires of different coils, the 
trouble is intensified. The whole armature may be burned out 
if the machine is not stopped in time. 



CARE OF DYNAMOS AND MOTORS. 425 

What is said of this class of short circuits applies to the arma- 
ture bars. A contact between contiguous ones represents short- 
circuiting within the limits of a coil. If remote armature bars 
are connected, it represents the more serious case of short-circuit- 
ing of different coils. 

Already a temporary cure for a broken coil has been described. 
This was the soldering together of its two commutator bars. 
Such soldering must never be done unless there is absolute cer- 
tainty of the break. It would be better to cut the wire and bend 
the ends apart, to make sure of disconnection, and then to solder 
as described. 

Sparking of the Commutator is a very serious evil. As the 
brush leaves a commutator bar, if all is not rightly adjusted, 
sparks will pass from the commutator bar to the brush. Every- 
thing in a direct-current dynamo or motor depends upon the 
accurate co-operation of the commutator and brushes. If spark- 
ing is allowed to go on, it deteriorates the metal parts of the com- 
mutator, and the edges of the bars cease to be straight and they 
lose their definition. The effect of this is to increase the spark- 
ing and with it the damage to the commutator until no remedy 
short of turning off the surface of the commutator in a lathe will 
restore the machine. 

The brushes may suffer in the same process of sparking. Their 
trimming and shaping is comparatively easy. The commutator 
is the critical thing. 

The sparking between a commutator and the brushes is injuri- 
ous to the commutator. It is trouble enough at the best to, keep 
a commutator in good order. To turn it down on a lathe, to trim 
the brushes and set them is a piece of work requiring time and 
trouble. The dynamo is also out of commission during this time. 
A commutator loses metal every time it is turned down, and if this 
is often necessary, it will sooner or later succumb. 

The main cause of sparking is very simply presented. Fol- 
lowed out to its full scope, the subject may become rather in- 
tricate. 

The cut, Fig. 311, represents conventionally a part of a com- 
mutator whose bars are lettered c d e f g. n' n gives the position 
of the end of the neutral line. In the position shown, the arma- 



426 



ELECTRICIANS' HANDY BOOK. 



ture windings indicated at W and X are sending current in the 
direction of the arrows. They lie in the left-hand half of the 
field. The coils U and Y lie in the right-hand half, and send 
current in the opposite direction. The currents join at the 
neutral point, and flow off through the hrush. 

It will be observed that one coil V is short-circuited and is 
"dead," because the brush bridges over the space between the 
commutator bars. As the armature turns, this coil is suddenly 
thrown into series with T and U and the whole of the right-hand 
division of the armature. Owing to self-induction, the coil V 
resists the passage of the current, and a spark goes across from 

E to the brush which has 
1 now left it. Such sparks 

ruin the commutator sur- 
face. 

But now suppose the 
brush advanced a little. 
When a coil is short-cir- 
cuited, it is no longer at 
the neutral point, but is 
in say the right-hand half 
of the armature. It is 
cutting lines of force, and 
electromotive force is 
g-enerated in it of the 
same polarity as that in 
the other coils of that 
half. As it leaves the brush, it is ready under the influence of 
that electromotive force once more to start into action and carry 
its current. The sparking now does not take place. 

If on the other hand the brushes are swung back, then the 
idle coil is still in the left-hand half. It cannot be called idle 
any more, as it is generating an opposite electromotive force, and 
it intensifies the sparking action by its own supplementary spark- 
ing. 

These facts must be firmly fixed in the mind. A neutral line 
exists in any active armature, which may or may not correspond 
with the position of the brushes. If the brushes are advanced 




Fig. 311.— Short-Circuiting of an 
Abmaxure Coil by a Brush. 



CARE OF DYNAMOS AND MOTORS, 427 

from this position, they carry the neutral line in their direction, 
but not as far as they themselves go. If the brushes are advanced, 
they therefore throw some coils into the wrong division of the 
armature. Such coils generate counter electromotive force and 
reduce the output. If the brushes are retarded, there is bad 
sparking; if they are advanced too far, it is less than if retarded. 

The ideal would be to have the brushes in the neutral line if 
there were no sparking there. 

If a dynamo has a weak field, the distortion of the field will be 
excessive. We have seen how the current induced in the coil V 
of Fig. 311 operates to prevent sparking. The distortion of the 
lines of force throws this coil into a weak portion of the field, and 
its action is greatly weakened. The sparking may be very hard 
to avoid in such case. A relatively strong field acts to prevent 
sparking. 

The fewer the commutator divisions on a given armature, the 
greater will be the electromotive force represented between any 
two of them, and the greater will be the inductance of the wind- 
ings included between them. One of the causes of sparking is 
disposed of by giving plenty of divisions to the commutator. 

The brushes keep the coil V of Fig. 311 short-circuited while it 
is passing the neutral line and electromotive force is being im- 
pressed upon it. This electromotive force as already described acts 
to prevent sparking. It is therefore an object to keep this coil 
short-circuited long enough to get it working before it is thrown 
into series with the others. One cause of sparking is too thin a 
brush or a badly-trimmed one. 

The idle coil must be in a strong field to be eflScient in prevent- 
ing sparking. The pole pieces should be so shaped as to give a 
strong field at the positions of the brushes just forward of the 
neutral line. 

Short-circuiting of one of the sections of the winding may cause 
sparking. The mere mechanical disturbance of shaking or jump- 
ing of the brushes is a cause of sparking. 

Starting a flachine. — Before starting a new machine or one 
which has been for some time out of service, the armature should 
be turned by hand to see if it is free to turn and has not got 
gummed bearings or too tight bearings. As it thus turns, the 



428 ELECTRICIANS' HANDY BOOK. 

windings should be observed to see if any wires rub against the 
pole pieces and if the axle of the armature is centered at both ends 
with respect to the cavity between the poles. 

The oiling apparatus must be examined to see if it is in per- 
fect condition, as lack of oil in a machine of such high-speed type 
may be disastrous. An iron oil can is not a good one to use, on 
account of the attraction the field may exert upon it. If oiling 
rings are used, they must be watched to see if they operate freely. 
In oiling, no drops of oil must be allowed to fall outside of the 
proper places. Especially none must touch the brush holder, 
windings, or commutator. 

In. starting, do it slowly, especially with new machines and 
new belting. It is well to run a machine for a while without 
load to ascertain if the mechanical parts are perfect and in ad- 
justment. This will show whether the bearings are slack or 
the armature out of balance. If the machine has to be moved 
along its base to tighten the belts, its axis must be kept at right 
angles to the line of belting. 

Starting a Dynamo. — The brushes should be lifted from the 
commutator, and only .brought down on the commutator after 
the full speed is attained. The brushes must not be pressed too 
strongly against the commutator. If metal brushes are used, cop- 
per dust is apt to be formed, which may short-circuit the commu- 
tator bars. After a run, when the machine goes out of action, 
always lift the brushes. 

Armature Running. — If a machine's armature is running at 
full speed, it should, if the power is thrown off, continue in mo- 
tion for a minute or more by its own inertia. 

Balancing of Armature. — An armature may be perfectly bal- 
anced for all positions when stationary, and yet not be in balance 
when in motion. Want of such balance causes vibration, which 
may shake a whole building. If a machine runs quietly, there 
is no need of further investigation of its rotary balance. To test 
it, however, the machine may be suspended in the air by its field 
eye-bolt and run as a motor, or less advisedly with a vertical belt. 
Any lack of balance will throw it into vibration. Vibration often 
produces sparking on the commutator. 

Cente <ng of the Armature. — The magnetic pull exercised by 



CARE OF DYNAMOS AND MOTORS. 429 

the field of a machine on its armature may pull the latter out of 
center by springing the shaft. The pull has been known to spring 
the field magnet frame so that it gripped the armature and held 
it mechanically, arresting its motion. This point may be investi- 
gated in a new machine by passing current through the field and 
observing the action on the armature and field. 

Armature Out of Center. — In bi-polar machines this trouble is 
of less account than in four-pole machines. In the latter, gen- 
erally four windings in parallel with each other are on the arma- 
ture. If the armature is out of center, the electromotive force 
impressed on the windings will be unequal. Local currents will 
occur to restore balance; the wires wi'l carry varying currents; 
sparking will ensue, and even on open circuit the armature may 
become heated. It follows that too great attention cannot be 
given ^o this point. 

Foucault or Eddy Currents may exist in the armature core, 
due to insufficient lamination, too thick disks, or to bad insulation 
between the disks. Nothing can be done for it except to rebuild 
the armature. They may exist in the armature windings, due to 
too massive conductors. Subdivided or laminated conductors 
tend to minimize the trouble; sinking the conductors in slots in 
the core, and rounding off the edges of the pole pieces, thus alter- 
ing the distribution of lines of force, also prevent it. The latter 
cure may introduce other troubles. Foucault currents are de- 
tected by the heat they produce. The hottest place is where they 
exist. 

Heating of Field Coils. — In shunt-wound machines this is 
liable to occur from too high a current being sent through the 
field. Every machine is built for a definite maximum voltage at 
a definite maximum, speed of rotation. If a machine operates 
with proper voltage, yet requires too high a speed for operation, 
or with proper speed has too low a voltage, the weakened field 
thus indicated will be apt to cause sparking at the commutator. 
But the reverse trouble of too low a speed for the given voltage 
or too high a voltage for the given speed indicates too strong a 
field. In charging storage batteries, the latter trouble may arise. 
Reducing the current is useless, as the field magnet current de- 
pends on the potential difference at the terminals. The voltage of 



430 



ELECTRICIANS' HANDY BOOK. 



the outer circuit must be reduced. The trouble makes itself evi- 
dent by heating of the field coils and pole pieces. 

If one field coil is hotter than the other, look for a short circuit 
in the colder coil. If there is such, it will cause an excess of 
current to pass through the field coils, thereby heating the per- 
fect one. 

Break in the Field Winding. — This simply brings a dynamo 
out of action. A shunt motor may be ruined by such an accident, 
as its speed will, unless restrained, increase until it wrecks the 
armature. The trouble is easily found by a galvanometer and 
dry battery or by a strong current and electric lamp. If no cur- 



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Figs. 313 and 313.— Short Circuits in Dynamo. 



rent will go through the magnet windings, there is evidently a 
break. Its repair may involve rewinding of the field. 

Short Circuits in Field Winding. — These are best detected by 
measuring the resistance of the field. They operate to weaken 
the field, to lower its resistance, so that it takes more current 
at equal potential and may give the remaining wires more load. 
The weakening of the field lowers the potential of the machine, 
and thus may often save the excessive load being given the wind- 
ings. The most complicated cases of short-circuiting in the field 
occur in compound-wound machines. Diagrams of some such 
accidents are given in which dotted lines indicate short circuits. 

Pig. 312 shows a short circuit between the middle of the shunt 
winding and the beginning of the series winding. In this case 
one half of the shunt coil is thrown out of action, and the other 



CARE OF DYNAMOS AND MOTORS. 



431 



half may get heated from excess of current. Such a short circuit 
affects the compounding of multipolar machines more than it 
does that of bipolar machines. It results in over-compounding. 

The next diagram, Fig. 313, shows the whole shunt winding 
thrown into parallel with the series winding. This is due to a 
short circuit between the beginning of both windings. The short 
circuit also operates to cut out the armature, and thus throw the 
machine out of action. 

In Fig. 314 is shown the outer end of the shunt winding con- 
nected by a short circuit with the inner end of the series winding. 
If the short circuit is of low resistance, it short-circuits the series 
winding, and the machine has to operate as if shunt-wound. 



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Figs. 314 and 315.— Short Circuits in Dynamo. 

Sometimes a shunt-wound machine has the outer end of the 
shunt winding connected to the inner end of the series winding. 
In such a machine a short circuit between the outer ends of the 
two coils will short-circuit the series coil, and the machine acts 
as if shunt-wound. This condition is shown in Fig. 315. The 
exact condition shown in Fig. 314 is brouglit about. 

Earthing Dynamo Frames. — The windings of a dynamo or mo- 
tor must be carefully insulated from the earth. The frame, on 
the other hand, is to be connected thereto. It is pretty sure to 
have such connection in any event. Small motors may be in- 
sulated altogether. To test grounds in the windings, a wire, with 
an incandescent lamp in circuit, may be connected to one of the 
bolts of the frame of the machine, and its other end brought 
into contact with any exposed part of the winding. The hands 



432 ELECTRICIANS' HANDY BOOK. 

should be carefully protected, either by using thickly-insulated 
wire or by India-rubber gloves. If the lamp becomes hot, a 
ground exists. Two lamps in series can be connected across the 
two main leads with the wire between them connected to the 
earth. If the windings on both legs of the field are in contact 
with the core, the lamps will light feebly. 

Short Circuits in Outer Circuit. — Sometimes a short circuit 
on the outer circuit may happen when no current is being de- 
livered, and the generating machinery is at rest. This takes 
away current from the shunt field circuit, and the generators 
will not build up a current. Nothing can be done except to find 
the trouble and rectify it. It is a very disagreeable occurrence, 
as the short circuit may never be even suspected until the time 
arrives for starting the generators affected by it. 

A short circuit on the outer circuit may be occasioned by neg- 
lect of customers to turn off their lamps or motors. A number 
of such left connected in parallel on an inactive circuit will inter- 
fere with the starting of the generator, just as if an accidental 
short circuit occurred between two leads. If lamps are kept 
burning and motors going until the current is shut off at the 
generating plant, they should be switched out by those in charge. 
Automatic cut-outs can be used for motors, which will cut them 
out when the current ceases. 

A temperature of 72° F. (40° C.) above the atmosphere is 
given by some authorities as allowable for dynamos and motors in 
action. 

Wrong Connections in Compound Dynamos. — When a com- 
pound-wound machine refuses to work, if a dynamo will not build 
up, and if a motor does not turn unless a short circuit such as 
has been just described can be detected, there is reason to suspect 
that the series coil of the field is wrongly connected. If inverted 
in connection, it will work in opposition to the shunt coil. This 
destroys the field excitation. Such wrong connection simply re- 
duces a compound dynamo to inaction. But in the case of a 
compound motor there is danger of an accident. It is necessary 
to use great care in starting compound-wound motors lest such 
an accident should occur. 

Turning Down a Commutator requires special care, as copper 



CARE OF DYNAMOS AND MOTORS. 433 

is a very tough metal, and the breaks between the bars may make 
the tool jump a little, causing irregularity in the work. A dia- 
mond-pointed tool taking a very fine cut is recommended. The 
fine cut is desirable, not only to secure finish, but to avoid using 
up the commutator. Were there enough of such work to be done, 
a milling machine would be useful. After the turning, the spaces 
between the bars should be brushed over to remove copper dust 
from the mica. 

Sandpapering and Smoothing a Commutator should be dohe 
when it is cold. If the mica tends to project, it will project more 
when the commutator is cold than when it is hot. This enables 
the sandpaper to better remove it. Another good point to be 
noted is that the increased projection of the mica causes its re- 
moval by sandpaper to be done with less expenditure of the 
copper of the commutator bars, which it is highly desirable to 
save. 

To Sandpaper a Commutator, a block of wood cut to the curve 
of the commutator, so as to take in at least one-third of its length, 
may be employed with which to apply the sandpaper. Tallow 
must be applied to the paper or armature surface, to enable the 
sandpaper to cut the mica. Rarely use a file, as this is apt to 
wear the surface of the commutator unevenly. If a commutator 
has to be turned off, care must be taken lest short circuits form 
by copper being crowded across the intervals between the bars. 

If one or more bars of the commutator show excess of wear, 
it indicates bad contact between the connection from the bars 
in question to their respective coils, or some other bad contact to 
be sought for in or about the coil in question. 

Filing a Commutator, — This is sometimes done. A bastard- 
cut file is used, and the armature is slowly turned during the 
filing. Filings must be carefully removed from between the 
commutator bars; a sharp hook-shaped tool will do this. A bel- 
lows will blow away all loose filings. 

Sliort Circuits. — A short circuit between the primary and 
secondary coils of alternators, alternating current motors or trans- 
formers, is dangerous to life. It may be brought about by light- 
ning stroke. It will destroy lamps, motors, and the like by 
the high potential thrown upon the line. The cases in which 



434 ELECTRICIANS' HANDY BOOK. 

this may occur are such as the following: The primary or 
high-tension line of a system may have a single ground connec- 
tion, and the low-tension or secondary may also have one. As 
long as the two circuits are insulated from each other, no harm 
need result, although a ground on a high-tension circuit is a 
perpetual menace to life. If by any cause such as a stroke of 
lightning an arc is started across from primary to secondary, 
this arc will connect electrically the two circuits, will burn out 
lamps and motor windings, and blow out fuses on such portions 
of the low-tension secondary circuit as lie between the arc and 
ground connection. 

Alternating-current dynamos are free from one source of trou- 
ble, the commutator. If short circuits are produced in their coils, 
the absence of a commutator involves the absence of sparking. 
The latter, while injurious to the commutator, has the attendant 
merit of being an indicator of trouble. There is no such indi- 
cator in alternators. Heating of the coil affected by the short 
circuit is the sign of trouble. 

Modern alternating-current generators generally have a re- 
volving field and stationary armature, sometimes called the 
stator. When the stationary armature is used, breaks in the 
windings very seldom occur, and are easily found by exploring 
with a source of current, and any current indicator. A dry cell 
and a simple galvanometer may suffice, if the machine is absolutely 
out of action and disconnected from every possible source of cur- 
rent. Such disconnection should be regarded as imperative in al- 
most all cases where explorations have to be conducted. 

Short circuits in the armature windings bring about local and 
dangerous heating. Such reduce also the current output of the 
generator, as the defective coil is no longer effective, and by its 
high current intensity operates to demagnetize the field. If the 
place where the windings are short-circuited has been found, and 
is accessible, a temporary repair may be made by pushing in 
mica between the wires. Sometimes the coil can be safely cut 
out and the neighboring coils can be connected across the in- 
terval. This is safe when there are enough coils on the arma- 
ture. Short circuits in modern alternators can hardly occur be- 
tween separate coils. 



CARE OF DYNAMOS AND MOTORS. 435 

Short Circuits Between Armature Windings and Frame are 

dangerous not only to the generator, but to the lives of the oper- 
atives if a ground circuit is on the line. A 200-volt tension has 
killed in several recorded cases. A common practice is to ground 
the framework of alternators. Then if a man touches the frame 
of a machine in which such dangerous short circuit exists, he is 
merely in parallel with a portion of the frame and receives no 
injury. Were the frame not grounded, he might be killed. If 
no ground circuit exists on the line, such a contact of windings 
and frame may remain undiscovered indefinitely unless watched 
for. It would be well to explore inactive and disconnected ma- 
chines to detect such. 

Alternator Brushes. — On an alternator never lift a brush 
while the machine is working, except where there are several in 
the set. Then one may be raised at a time, some being kept al- 
ways in contact. It is bad policy to work much around an al- 
ternator when it is in action. 

Trouble in Rotors of Alternators may be caused by bad condi- 
tion of the collecting rings, which may be dirty, unevenly worn, 
or oval. A periodic breaking of the circuit at the brushes due 
to such causes will occasion sparking. The cure is to attend to 
the rings and brushes and remedy their defects. The large num- 
ber of poles of the usual type of alternators makes short-circuit- 
ing unlikely in them, as the copper is distributed in smaller 
masses, and the insulation is not so subject to wear. Another 
effect of this subdivision of windings is that if one winding 
gives out, it can often be cut out and short-circuited, and the 
machine kept in action until the chance occurs to replace or re- 
pair the defective coil. Cutting out a pole merely exacts a little 
higher magnetizing current, and no sparking results. 

5elf=Starting One=Phase flotor.— To make a one-phase alter- 
nating-current motor self-starting, a capacity is introduced into 
the main exciting circuit or an inductance into the shunt circuit. 
This splits the current and delivers a two-phase current to the 
motor, establishing a rotatory field. One of the most frequent 
sources of trouble is to be found in this capacity or inductance. 
If either of these is out of order, the current will not be properly 
split, and the motor will not start. A condenser with iron plates 



436 ELECTRICIANS' HANDY BOOK. 

immersed in caustic-soda solution is sometimes used as a starting 
capacity. By evaporation it is liable to change. The inductive 
coil is to be preferred to such a capacity apparatus. 

Local Heating of the Windings of the Stator in an induction 
motor indicates a double short circuit either in a single coil or in 
two neighboring coils. If wound for Y distribution, an interrup- 
tion of one phase will interfere with the running of the machine. 
If the load is light, it may go on as a synchronous motor. Some- 
times the beginning and end of a coil are interchanged in their 
connection, so as to reduce the phase difference to 60°. This inter- 
feres with the running of a three-phase Y-connected motor. 

Induction flotor Rotors. — The short-circuited disconnected ro- 
tor of induction motors seldom gives trouble. In the older type 
the rotor would sometimes become so hot as to melt the solder 
on the connections of the windings. This by opening the circuit 
would bring the machine to rest. For this reason it is the best 
practice to use no solder on the joints, but by hard metal coup- 
lings or brazing to secure heat-proof joints. 

Synchronous Motors, whether single or polyphase, should be 
speeded up before loading, and the load should be gradually ap- 
plied only after the full speed has been attained. They must not 
be overloaded, or they will be brought to rest. These motors have 
the feature of maintaining a constant speed as long as they run. 

Polyphase Induction Motors, which can endure an overload 
within certain limits, lose in speed as the load is increased, but 
are self-starting even with a load. 

Field riagnets of Alternators often constitute the rotating 
part, which exposes their windings to a certain strain and wear, 
from which they are exempt in direct-current machines. But 
their windings per pole are generally lighter than in direct cur- 
rent machines, which operates to save them from the action of 
centrifugal force and shocks and strains at starting and stopping. 
If sparking appears at the collecting rings and brushes, it may 
be due to periodical breaking of the field circuit, bad material of 
rings or brushes, dirt or oval rings. If the trouble is in one 
magnet pole, it can be short-circuited as a temporary expedient. 

Two=Phase Operation. — If a two-phase station is operated by 
two single-phase transformers in parallel with each other, if one 



CARE OF DYNAIIOS AND MOTORS. 437 

breaks down the station must be run on one phase until repairs 
are effected or the transformer is replaced. If a three-phase sta: 
lion is operated by three single-phase transformers in mesh or 
delta connection, and one breaks down, the station can still be 
run three-phase with two transformers, although on full load they 
will be greatly overloaded. 

Breakdowns in Transformers seldom occur. The principal 
omn to be apprehended is a short circuit in the high-tension wind- 
ing. This in a dry transformer will slowly carbonize the insula- 
tion, and short-circuit a more or less considerable part of the 
winding. With disk-wound transformers, such as those using 
pancake coils, this trouble is minimized. If the short circuit 
operates to throw many turns out of action, the potential of the 
low-tensicn coils will increase perceptibly if such are the sec- 
ondary coils. This is an indication of trouble which will be seen 
on the voltmeter or possibly in lamps. The transformer will be 
caused to rise in temperature, and will pass more current when 
unloaded than it should under normal conditions. If it is a step- 
up transformer, a short circuit in the high-tension secondary will 
lower the potential. 

Care of Transformers. — These must be kept dry. If immersed 
in oil, the oil will take care of them. If air-cooled transformers 
are to be stored in a place where moisture is to be feared, chlor- 
ide of calcium may be placed on trays or saucers inside the cases. 
This has to be renewed as it gets moist. Quicklime is also avail- 
able for the same purpose. These precautions do not apply to dry 
storage apartments. Dust is injurious especially to oil-cooled 
transformers, as it tends to thicken the oil. Dust may make short 
circuits. 

Transformers long out of use must be started with the precau- 
tions exacted for new ones. 

As long as transformers are working, they should not be 
touched. If anything is to be done to them, they should be dis- 
connected. This applies especijilly to operations on the high-ten- 
sion side, such as putting in safety fuses. 

Oil for Filling Transformers is a petroleum product specially 
prepared for the purpose. It should have a very high flashing 
point; 500° F. (260° C.) is given as a proper temperature of 



438 ELECTRICIANS' HANDY BOOK. 

flash. Before pouring it into the tanks of the transformers, it 
.shoiild.be heated to 160° F. (71° C.) It must be poured or 
pumped in carefully, and must be kept off the cable ends. It 
must rise over the tops of the coils. The insulation absorbs 
more or less of the oil, on which account it is advisable to in- 
spect a newly-filled transformer from time to time, to see if it 
needs more oil. After three or four weeks all should be absorbed 
that will be taken up. Oil filling must be done under cover if 
there is. any fear of water getting in. Every two or three years, 
renewal of the oil is advisable. New transformers should be 
inspected, to see if any foreign bodies have lodged within them. 
Such should be removed. 

Moisture in Transformers must be watched for carefully in 
their first run of ten or twelve hours, as any present is expelled 
during this period and there is danger of its collecting into drops. 
If such appear, the transformer must be cut out of the circuit and 
dried as well as possible with a dry cloth or blotting paper. After 
such partial drying the heat of the core will complete the oper- 
ation rapidly. 

Inspection of Transformers. — Every four weeks transformers 
should be inspected. The high- and low-tension safety fuses 
should be examined. After dusting it off the cover should be 
removed, the contents cleaned, and the capacity of the safety 
fuses should be noted. 

Short Circuits in Transformers. — If a transformer strikes 
across from high tension to low tension or to the case, supposed 
in this instance to be grounded, the safety fuses should melt 
and cut out the transformer. Short circuits in the same coil, 
which are generally to be apprehended in the high-tension coils, 
are not so easily detected. The noise of the transformer is apt 
to increase in such case, the oil gets hot, and the iron case is 
warmer than usual to the hand. The heat impairs the quality 
of the oil. The transformer should be disconnected and repaired. 
There is even a possibility of an explosion, as the heated oil may 
give off gas enough to be inflamed on the melting of a safety fuse. 

Transformers need to be well protected from lightning. 



CHAPTER XXV. 

STATION NOTES. 

Temperature of Dynamo or Motor.— It is not easy to accurately 
determine the temperature of the coils of a machine. The best 
that can be done with ordinary appliances is to put a thermom- 
eter as well in contact as possible with the part to be tested, and 
to cover the place of contact with cloths to keep in the heat. The 
cloth must be so disposed as to form a little chamber for the 
thermometer bulb. The temperature of 122° P. (50° C.) is given 
as the maximum allowable. 

Cleaning New flachine. — A new machine should be cleaned 
before being set at work. Chamois is a good material to wipe it 
with, as it leaves no threads or lint hanging to the bolt heads, 
nuts, and screws of the machine. Dust can be blown out of inac- 
cessible parts, as among the end wires back of the commutator, 
with a bellows. Anything in the shape of filings may go to short- 
circuit adjacent commutator bars. 

Interchangeability of Parts is expected almost as a matter of 
course in buying a standard American machine. It is of the 
greatest convenience, and often of the greatest importance, to be 
able to get* parts on short notice. But the moment this system 
acts to discourage improvements, it exercises a sterilizing effect. 
A first-class manufacturing company should keep in stock a full 
line of parts of all their principal machines, but the inevitable 
accumulation of parts should not discourage the course of im- 
provement. 

Cotton Waste. — Never use cotton waste in cleaning a machine, 
as threads from it will catch in and stick to the commutator and 
other surfaces. 

Access of Air. — Air is so constant a cooling agent, that free 
access of it to motors and dynamos is highly to be recommended. 

439 



440 ELEGTRICIAI18' HA2\WY BOOK. 

Boxing up or inclosing in closets of dynamos and motors, except 
for very intermittent service, is to be condemned. 

Oiling. — Before starting a machine, turn the armature by hand. 
This will disclose any friction. This precaution should be taken 
for generators or motors, unless they are in such constant use 
that the operative is certain that their oil feed is in perfect order. 
Want of oil will wear the journal boxes, and throw the armature 
out of center. The greatest care of the oil-feeding apparatus is 
requisite, because this class of machinery runs at high velocity. 
The best and purest oil should be used, and once a satisfactory oil 
is found, its use should be adhered to. If the oil is fed by wicks, 
the drip of oil from the bearings will show that they are in order. 
Oil once used should be filtered or water-purified before being used 
a second time. Oiling rings must be watched to see if they move 
properly around the axle. When the old oil gets thick, new must 
be added after drawing off the old. Before adding the new oil it 
is a good plan to wash out the oil trough with kerosene oil. A 
small syringe is useful for this purpose. 

Oil should carefully be kept off the brush holders, commutator 
surface and wire windings of field and armature. 

Ring Oiling is much used. Rings several times the diameter 
of the axle hang on it. Their lower portions dip into a tank of 
oil. As the shaft revolves, they travel around it and feed oil 
to its upper surface from the tank in which they dip. 

Bearings.— If new machines are started without due attention 
being given to their bearings, heating, burning fast, or even melt- 
ing (if babbitted) of the journals is liable to occur. A good 
plan is to pour kerosene through the bearings until it comes out 
clean. This leaves them ready for lubrication, by washing out 
dust or dirt which may have collected. Too stiff or tight belts 
cause heating of the journals. These are especially to be antici- 
pated in new installations. If belts have to be tightened, it 
should be done slowly and a little cit a time, with periods of run- 
ning between, until they are just right. 

Belts too tightly stretched may even occasion melting of the 
bearings. 

Bearings are generally so constructed that with proper manage- 
ment they will not heat. Insufficient oil, too thick oil which does 



STATION NOTES. 441 

not penetrate, dirt and dust getting into the bearings, are causes 
of heating. Cleaning with l^erosene followed by the application 
of good lubricating oil is the cure. 

Safety Fuses should be inspected to see if they are tightly 
screwed down or clamped, and if their contact faces are clean. 

Insulation of Windings. — Watch for bare spots or weak spots 
on the insulation of the wires of the winding. If any such appear, 
they must be taped or insulated in some way. 

Broken Wires, even if thickly insulated, can be detected by 
the feeling, when the wire is slightly bent or moved. If the 
insulation shows signs of burning or of overheating, a fracture 
may be suspected there. 

Soldering. — Never use acid in soldering wires together. Anti- 
corrosive soldering fluxes are sold, which operate on iron and 
copper as well as acid, and whose use is not followed by any bad 
after effects of corrosion. 

Nails, Tacks, and iron Filings may do harm by being at- 
tracted to a machine by its field magnets. Bronze spanners are 
recommended in place of iron ones. An iron object suddenly 
drawn to the field may, by rubbing against the armature or strik- 
ing the screw heads or windings, near the commutator, do harm. 

Screws in Binding Posts and connections should be looked 
after; imperatively so if their color indicates overheating. 

Covering Machines, dynamos and motors when not running is 
recommended. 

Emergency and Danger Signals. — A sudden rise of voltage 
or of current, sudden sparking at the commutator or elsewhere, 
heating of the windings, or smell of heated insulation should be 
a danger signal, and the current should be cut off from the ma- 
chine showing any such manifestation. A working test of dan- 
gerous heating is the ability of the hand to stand it. If the 
hand qan be held on the windings, they are reasonably safe from 
overheating. For each dynamo the allowable heating should be 
learned, so that by holding the hand on it, any unusual heating 
can be detected. 

In throwing open the main switch in such a case, do it quickly 
to avoid arcing, and have the engine watched to prevent its racing 
as the load is taken off. 



142 ELECTRICIANS' HANDY BOOK, 

If a safety fuse blows out, do not put in a new one until the 
cause of the blowing out is known and overcome. Always use 
the regular fuse wire. Never substitute anything except in emer- 
gency. 

Keep all switches perfectly clean as regards their contact sur- 
faces especially. 

Whenever a machine goes out of action, it should be examined 
and cleaned. If any oil has fallen on the coils, it should be wiped 
off, and oily places generally should be cleaned. Dampness is 
bad for machines, and dripping water may make dangerous short 
circuits. 

Rheostats and resistances are often strongly heated in use, so 
no combustible substance, oily waste especially, should be allowed 
near them. 

Forgetfulness and Negligence are justly said to be the cause 
of many troubles. Thus, in stopping a motor, or in case cur- 
rent is cut ofC without notification, it is absolutely necessary to 
bring the handle of the starting box back to the starting position, 
so as to throw in the full starting resistance in series with the 
armature, to save it from burning out when the curi-ent is again 
turned on. 

Keep One Hand in Your Pocket is an old and a good rule to 
follow when working around motors and dynamos. If good new 
India-rubber shoes are worn, the safety is increased. When 
work must be done around a high-tension active machine, such 
precautions as wearing India-rubber shoes are eminently proper 
and not at all extreme. 

Treatment of Electric Shock. — The first thing to be done 
when a man is injured by contact with an electric circuit is to get 
him out of contact therewith. If possible, open the circuit or 
stop the generator. Drag the man away from the conductor or 
conductors. Do not touch his hand or any part of his skin in 
doing this, handling his clothes only. If they are wet, throw a 
dry towel or other cloth over them before touching them. Other- 
wise, the one helping may be shocked. Especially dangerous is 
touching the surface of the body directly. 

A physician should be called as quickly as possible. It is a 
grave responsibility to neglect this. Do your utmost to rescue 



STATION NOTES. 443 

the man, but get professional help instantly or as soon as prac- 
ticable. 

If the man is in contact with one conductor and cannot be re- 
leased, break the ground connection of his body. Push coats, a 
blanket, wooden boards, and the like under him. In doing this, 
stand upon a dry board or coat; if you have them, put on India- 
rubber gloves before handling even his clothes. When thoroughly 
insulated from the ground, the rescuer can try to open the man's 
hand if that is cramped upon the conductor. This is very dan- 
gerous unless India-rubber gloves are worn or a dry towel is 
used to protect the one doing it. 

The two leads can be short-circuited by throwing a chain or 
bare wire across them. This undoes the effect of a ground. It is 
a rather desperate thing to do. 

When the senseless man is free from the contact, remove cloth- 
ing from around his neck and his waist, so that he will be free 
to exercise his breathing organs and muscles of the trunk and 
diaphragm. He is then to be treated as if he were to be resusci- 
tated from drowning. Artificial breathing is to be started. 

Place him on his back, with a pillow or other support under 
his neck and shoulders, not under his head. His head will drop 
back, and the top will almost touch the floor. Open his mouth 
and hold it open, seize the tongue between finger and thumb 
with a handkerchief between, and draw it slowly forward. The 
root of the tongue must move outward as this is done. It is 
useless to merely elongate the tongue itself. When satisfied that 
this action has taken place, let the tongue slowly go back. Repeat 
this double movement about fifteen times a minute. 

While this is being done, a second person can assist the breath- 
ing by moving the arms up and down. He should kneel back 
of the man's head with face toward him, seize his arms at the 
forearms, press them strongly against the breast-bone, and then 
lift them slowly in the arc of a circle over his head, and after 
a short pause return them and press them against the chest 
again. 

Let the man manipulating the tongue call "one" as he draws 
the tongue forward. The arms are now pressed against the chest. 
This represents expiration of the breath. "Two" is called, and 



444 ELECTRICIANS' HANDY BOOK. 

the tongue is slowly allowed to go back and the arms are raised 
as described. This represents inspiration. Again "one" is called, 
and the tongue is drawn out and the arms returned. Thus every 
four seconds the double movement is repeated, arm motion and 
tongue motion keeping time with each other. 

It is easy to experiment with one's own tongue, and thus study 
the effect of manipulating it. It will be found that a drawing 
down over the chin as well as outward opens the windpipe. 

The first sign of resuscitation is natural inspiration. See that 
the tongue is drawn forward, so as not to hinder the access of air 
to the lungs. By no means pursue the movement of expiration 
until the incipient natural inspiration is completed. Keep the 
arms raised and tongue drawn forward until it ceases. Then re- 
peat the expiratory movement. Do not get excited, but do all 
slowly and with clocklike regularity. When he breathes regu- 
larly, he may be brought into a more upright position, and re- 
moved to a bed or other better resting place. Before this a phy- 
sician should be at hand to treat him further. 



CHAPTER XXVI. 

SWITCHBOARDS. 

Switchboards. — These are vertical partitions, generally made 
of marble, on one side of which are installed rheostats, bus-bars, 
voltmeter switches, and connections of station apparatus, and on 
whose other side are installed handles for operating the rheostats 
and voltmeter switches, automatic cut-outs, safety fuses, switches, 
voltmeters, and other appliances. 

The general system is to make the switchboard in panels. Each 
panel is about two feet wide and six to eight feet high. It stands 
vertically, being supported by braces at its top running back to 
the wall of the building, thus having a space behind it, so that 
its back is accessible. Any desired number of panels are joined 
side by side. 

Panels. — Of panels there are various kinds. Some are for mo- 
tor control, others for dynamo running, others for operating the 
outer circuit, others for storage-battery charging and the like. 
As many as are required by the station are set up side by side, 
so as to present a long front. The variety of panel chosen de- 
pends on the work it is to do. 

The description of a switchboard is little more than a descrip- 
tion of the apparatus which it carries. Every engineer must 
study the switchboards in his own station, as the varieties are 
numerous. 

The General Electric Company manufactures a line of standard 
panels, which are so varied in design as to cover almost any de- 
sired case. 

The front and rear views of a generator switchboard panel are 
given in Figs. 316 and 317. Toward the bottom are triple con- 
tact switches, which close both leads of the circuit, and also the 
equalizing conductor it compound dynamos in parallel are used. 

445 



446 



ELECTRICIANS' HANDY BOOK. 



On the real the horizontal flat conductors are bus-bars. On the 
sides of the rear view are seen rheostats operated by handles in 
front. Voltmeters are placed near the top. The central connection 




fimr^^T^' 



C rn 




Figs. 316 and 317.— Front and Rear Views of a Direct Current 
Switchboard Panel,. 



of the switches, intended for the equalizer, is left unconnected if 

the generators controlled by them are shunt-wound. Reference 

may here be made to page 403, showing the use of the equalizer. 

Switchboard panels are named, from their uses, generator pan- 



SWITCHBOARDS. 



447 



els or feeder panels, and also from the current they are arranged 
for, whether direct or alternating. 

Air Switches. — Of these there are a large variety. The prin- 
cipal working contact made by closing them is a knife-edge 
contact, made by a thin copper bar on the switch going edgewise 
between two leaves of copper that spring against it. This makes 
one of the best kinds of connection, but in breaking it an arc is 
apt to form. To prevent this, switches are often provided with 
auxiliary contact blocks of carbon. These are so arranged as to 
be the first to make and last to open. An arc between carbon sur- 
faces will not draw out as will one between metal surfaces, and 
if it does form, it does no harm. Metal electrodes are burned and 
rapidly injured by arcs. The subject 
comes up again under the automatic 
circuit breakers. 

Pig. 318 shows a two-pole knife- 
blade switch for use on switchboards. 
It has metallic contacts only. 

Oil Switches.— To avoid the for- 
mation of arcs, and to insure definite 
opening of a circuit when the switch 
is opened, oil switches are employed. 
These have the part of their mech- 
anism which opens and closes the 
circuit immersed in oil. This fea- 
ture insures definite action, and is 
particularly applied to high-voltage alternating-current switches. 

The principle of construction is shown in Fig. 319. On the 
right and left hand are seen two metallic rods, which descend 
through insulating blocks and carry springs at their lower end 
projecting therefrom. Through an insulating block another me- 
tallic rod descends between these two, and carries at its lower end 
a cross piece with beveled carbon contacts C C, facing upward. 
This rod moves up and down. It is connected to one lead of the 
circuit; both side rods are connected to the other. When the 
central rod is raised, its carbon blocks enter between the springs 
and make the contact, closing the circuit. When lowered, it opens 
the circuit. A tank of oil, indicated in section in the diagram, 
contains oil in which the mechanism shown is immersed. 




Fia. 318.— Two-Pole Switch. 



448 



ELECTRICIANS' HANDY BOOK. 



ra 



The tank is placed behind the switchboard. A handle on the 
front of the switchboard raises and lowers the central rod. 

Overload and Underload Cut=Outs.— These are of two types, 
safety fuses and mechanical cut-outs. The subject is more ac- 
curately treated than formerly, and cut-outs are now expected to 
operate with a high degree of accuracy. In ordinary parallel 
circuits overload cut-outs are placed so as to open their portion 
of the circuit if the current becomes too strong. In series cir- 
cuits the cut-outs are arranged 
to operate by short-circuiting 
any lamp which may be ex- 
tinguished. The object is to 
preserve the continuity of the 
circuit; it is exactly the oppo- 
site of the function of a paral- 
lel-circuit cut-out. The under- 
load cut-out operates to open 
a circuit when the current 
weakens, ceases, or is reversed. 
Such an appliance is used in 
charging storage batteries. If 
the current falls to zero, it in- 
dicates that the counter elec- 
tromotive force of the battery 
IS equal to the electromotive 
force of the charging appli- 
ance or circuit, and there is 
danger that it may increase, 
when current would flow back from the battery and discharge it. 
The underload circuit breaker opens the circuit as the current falls 
to zero. Cut-out and circuit breaker are practically synonymous. 
Safety Fuses are strips of fusible metal, whose resistance 
will develop heat enough to melt when a current goes through it 
too strong for the rest of the circuit. An ordinary type of fuse is 
a wire or strip of a specified cross section and length with ears 
at the ends by which it is screwed down to the circuit terminals. 
A very usual system is to mount it on a block of porcelain. The 
lugs or ears at the ends should be clean before it is inserted. 



Fig. 319.-OIL Switch. 



SWITCHBOARDS. 



449 



They may be scraped with a knife or may be filed or sandpapered 
before being put in place. The terminals to which they are screw- 
ed should also be bright. In screwing the screws in or out, care 
must be exercised to avoid making a short circuit with the screw 
driver. Sometimes the fuse is mounted in a screw cap, and is 
screwed on a plug in somewhat the way an incandescent lamp is 
screwed to its socket. Screwing the cap into place makes the con- 
tact of the ends of the switch with the circuit terminals. The 





Figs. 330 and 321 —Safety Fupe and Holder. 



plug cut-out, as it is called, is a very safe form. If the short 
circuit still exists, the socket being screwed in the plug will 
simply blow out again without the operator's incurring any dan- 
ger. The inclosed fuse is a fusible wire or metal strip embedded 
in porous non-combustible material within a tube. It is sprung 
into place between clips in some constructions, which is a very 
convenient and safe arrangement. The fuse being protected from 
the air is supposed to be more constant in its action than is the 
exposed fuse. It is also claimed that it does not blow out so 



450 



ELECTRICIAN &' HANDY BOOK. 



quickly, requiring a sensible time to fuse. This is an advantage 
generally, as an excess of current lasting only a second does no 
harm. The fuse does its work better if it is a little slow about 
blowing out than if it yields instantly. The inclosed fuse does 




Fig. 322 — I.T.E. OvERT.OAD Circuit Breaker. 



not throw melted metal about, which is another advantage. In- 
closed fuses in and out of their clips are shown in Figs. 320 and 
321. A small wire in parallel with the main fuse is exposed in 
a little circle seen on the surface of the fuse case. If the fuse 
melts this also melts, so that the operative knows what has hap- 
pened. 



SWITCHBOARDS. 451 

Overload Circuit Breakers. — These are switches operated by 
electro-magnets directly or indirectly, so as to open if the cur- 
rent becomes too strong. 

The cut, Fig. 322, shows a section of the I. T. E. circuit breaker, 
whose initials stand for inverse time element. The instrument 
is shown with the switch closed, and connection made by knife- 
blade contact. The switch arm is pivoted at the bottom and 
works in a vertical plane. When it is pushed up into the vertical 
position as shown, it is held there by a catch, seen just below the 
handle. The upper end is forced outward by a horizontal plunger 
actuated by a spiral spring. This is contained in a tube at the 
top of the apparatus. In the illustration part of the tube is 
seen broken or cut away, so' as to show the plunger. The full 
current goes through the magnetizing coil back of the pivoted 
switchbar. The plunger armature of the coil is shown partly 
below it, and with its upper end within it. Above the armature 
at some distance from it is a rod which if lifted trips the catch 
which holds the switchbar in place. Its upper end bears con- 
stantly against or almost touches the back of the catch. If the 
current becomes too strong, the armature is drawn upward with 
increasing velocity, and strikes the loose plunger a sharp blow, 
driving it upward. This releases the switchbar by tripping the 
catch. The horizontal plunger, forced out by its spring, pushes 
the switchbar backward, breaks the knife-blade contacts, and 
the bar falls back into a position about 45° above the horizontal, 
resting on the bracket or stop seen behind it. The position of 
the armature is regulated by a screw below it with jam nut, all 
of which is shown in the cut. This can regulate the circuit 
breaker so that it will open at different current strengths. 

It is evident that the greater the excess of current, the more 
rapidly will the opening occur. The armature is more strongly 
attracted as it rises. Therefore a very small excess of current 
will operate it, because if a current is strong enough to lift the 
plunger from its seat, it will act upon it more energetically from 
the moment it leaves its seat and rises toward the coil. 

The circuit breaker shown in Fig. 322a operates on a slightly 
different principle. If the handle projecting to the right is 
pushed upward, the circuit is opened. Two contacts, one of 



452 



ELECTRICIANS' HANDY BOOK. 



metal and one of carbon, the carbon placed directly above the 
metal contact, are opened if the handle is pushed up. The con- 
tacts are shown closed in the full lines of the cut.. The dotted 
lines show the position of the movable parts of the contacts 
when they are opened by pushing up the handle. The circuit 
can be opened and closed by hand. To give it the overload 



r 




Fig. 323o.— G.E.Co. Overload Circuit 
Breaker. 



Fig. 323.— Magnetic Release Under- 
load CiRCTJiT Breaker. 



automatic action an electro-magnet is attached to the base of the 
apparatus, which attracts, when excited, a pivoted armature. 
"When attracted it flies up, strikes the handle, driving it up, and 
opens both contacts, the carbon one last. The pivoted armature 
is seen in the cut just below the switch arm and electro-magnet. 
An adjusting screw is provided to adjust it to act at any desired 
current within the range of its action. 

Underload Circuit Breakers are designed to open a circuit 
if the current weakens. This is often requisite, especially in 
charging storage batteries. A weakening of the current indi- 



SWITCHBOARDS. 



453 



cates increased counter electromotive force in the battery. If 
this increases beyond a certain amount, the battery will discharge 
itself through the dynamo and drive the latter as a motor. 

Magnetic Release Underload Circuit Breaker.— This is a form 
used often on motor starting boxes, as explained elsewhere. The 
illustration. Fig. 323, shows a switch-arm held in place by an 
electro-magnet against the attraction of a spring which pulls it 
back. A series of contact studs are shown. In the position shown 
in the cut, one is under its end, and current goes through the 
magnet. If the current weakens, the spring will prevail and will 
jerk the handle back and 
open the circuit. The 
spring is not drawn of 
the full length. Often a 
spiral spring like a heavy 
clock spring is used at 
the pivot end of the 
switchbar instead of such 
a one as that in the 
figure. 

Mechanical Release 
Underload Circuit 
B r eakers.— These are 
constructed on the lines 
of the overload circuit 
breaker just described. 
The principle is shown in 
Fig. 324. A pivoted bar 

carrying an armature R is held in the position shown in the 
dotted lines against a spring, omitted in the cut, by a magnet M 
actuated by the working current. When the current ceases, the 
magnet releases its armature, which, drawn back by the spring, 
trips the catch a and releases the switchbar. Often both overload 
and underload coils, each with its own tripping mechanism, are 
embodied in the same switch. To release at no load, the magnet 
is in series with the main current. At the handle end of the 
switchbar is a pivoted lever. This is pulled back by hand when 
the switch is to be set. Its projecting end pushes up the bar. 




Fig. 324.— Underload MECHANicAii 
Release Circuit Breaker. 



454 ELECTRICIANS' HANDY BOOK. 

so that its armature R is pushed up against the magnet M. The 
catch a then locks and the pivoted lever at H drops out of action. 
A is a metal contact and B B are carbon contacts. The contact A 
opens first, and then B B open. This breaking the contact on car- 
bon is done to avoid the formation of a metallic arc on the 
break, as spoken of in the case of switches. 

Reverse Current Circuit Breaker. — In this type the contact is 
kept closed as long as a difference of potential exists on the line, 
although it may be on open circuit. A shunt coil surrounds the 
magnet core, to give the reverse current release. If any potential 
difference is maintained on the leads of the circuit, a current 
goes through the shunt circuit and keeps the magnet excited, so 
that it cannot release its armature. A reversal of current de- 
magnetizes it for an instant; during the change of polarity the 
armature drops and strikes the switchbar catch. The bar drops 
and opens the circuit. 

Combined Circuit Breakers. — It is very usual to combine two 
circuit breakers in one, an overload and underload one, both actu- 
ated by the same outer circuit. Such circuit breakers as shown 
in Figs. 322 and 324 are often combined in one. 

Other contacts than the knife blade are used. Sometimes a 
series of leaves of laminated copper slightly bent, something like 
a carriage spring, are arranged to make contact by pressing their 
ends against a flat surface of copper. 

Circuit Breakers as Switches. — Frequently circuit breakers 
are used as switches, regular switches being dispensed with. 
Whole switchboards are fitted up in this way. 

Alternating = Current Potential Regulator.— This consists of 
an induction coil whose secondary is tapped at a number of points. 
For each tap a contact is provided on the dial face of the appar- 
atus shown in Fig. 325. The contacts are arranged in a circle, 
and an arm turns on the same center, so as to make connection 
with them in so doing. The arrangement forms a multipoint 
switch. By cutting in or out parts of the secondary by means 
of this switch, the potential of the secondary circuit is changed. 

The potential of feeders is controlled by the regulator, which 
adds its voltage to that already impressed by the alternator 
upon the feeder circuit. 



SWITCHBOARDS. 



455 



Reversing switches are provided on tlie faces, so that the poten- 
tial of the regulator may work in counter and lower the voltage 
of the feeder circuit if this effect is required. 

One lead from the generator bus-bar goes straight to the dis- 
trict. The other lead goes to the reversing switch, and passes 
through some of the turns of the secondary of the regulator coil. 
The number it passes through depends upon the position of the 




Fig. 325.— Alternating 

Cfrkent Potential 

Regulator. 



L h-' 




W^I^ 






4V: 



Fig. 326.— Direct Current 
Ground Indicator. 



multipoint switch bar. If the switch is set in one direction, the 
regulator adds potential to the circuit. If set in the other direc- 
tion, it subtracts potential. The primary coil is connected across 
the two main leads before the regulator is reached. 

In some stations the generator is run at potential sufficient 
only for the line having the smallest drop, and regulators are 
used to add to it. The action is like that of boosters in direct 
current work. Sometimes the original potential is enough for the 
highest drop of the system, and the regulator with reversed switch 
lowers it, acting like a crusher in direct-current work. 



456 



ELECTRICIANS' HANDY BOOK. 



Direct= Current Ground Indicator. — If two wires of a lighting 
or power circuit, shown in Fig. 326, are connected with each 
other through two lamps, L L, each one of the voltage adapted 
to the circuit, they will show a dull red. This is because being 
in series they will receive far too little current. Their com- 
bined voltage is twice that of the circuit. From the conductor 
at C between the lamps a connection f is made to the ground. 
A ground plate or water pipe may be used for this purpose. 

If there is no ground upon the circuit, the lamps will take one- 










L<r>J 



i^if^^ 






Figs. 337 and 328.— Alternating Current Ground Indicator. 




half their normal current, and will show a dull red as described. 
If a ground should occur on either line, one of the lamps will be 
short-circuited by the accidental ground and the ground between 
the lamps and will decrease in brightness, while the other will 
increase perhaps nearly to its normal. Generally speaking, the 
lamp which is reduced in illuminating power is the one connected 
to the grounded line. 

Alternating - Current Ground Indicator. — Alternating-current 
lamps in permanent connection are not favorite ground indicators, 
as they necessitate the grounding of the circuit. By a switch and 
transformers lamps can be arranged to show a ground whenever 



SWITCHBOARDS. 



457 



the switch is closed. The arrangements are shown in the dia- 
grams, Figs. 327 and 328. One embodies the use of two coils and 
two lamps, L L; the other that of a 
single lamp, L. The grounding is 
indicated by T. The single-lamp 
arrangement does everything which 
the double-lamp arrangement does. 
Ground Alarm.— Neither of these 
is an alarm properly speaking. They 
disclose nothing until the switch is 
closed. This is an undesirable 
feature. The next arrangement, 
Fig. 329, is a constant-alarm appar- 
atus. At C C are two plates of 
metal forming condensers. They 
are connected through m n as shown 
with a "telephone t on the line going 
to the ground T. As long as there 
is no ground on the line, no cur- 
rent goes through the telephone. 

If a ground occurs, a current goes through it, causing it to pro 
duce a humming sound loud enough to be heard through a good 
sized room. 




Fig, 329.— Telephonic 
Ground Indicator for Al- 
ternating Current Circuit. 



CHAPTER XXVII. 

VOLTMETERS AND AMMETERS. 

The Voltmeter is a galvanometer whose scale is graduated to 
read directly the potential difference at its terminals in volts. 
Certain conditions which it has to fulfill are determined by the 
use it is to be put to. It must be so constructed as to give the 
voltage between different points of a circuit over which a cur- 
rent is passing. This it must do without affecting appreciably 
the current. As it has to be connected in parallel with the por- 
tion of the circuit to be tested, it follows that a certain propor- 
tion of the original current will pass through the voltmeter, and 
the main current will be diminished by that amount. Therefore 
it must operate with an exceedingly small current — one so small 
that it will count for nothing. 

Voltmeters are used principally in engineering practice and 
on reasonably large current circuits. The current which goes 
through the voltmeter in such cases is treated as infinitely 
small. Other cases arise in laboratory practice where the cur- 
rent passing through the coil of the instrument has to be taken 
into consideration. 

One type of voltmeter is actuated by coils of wire through 
which a very small current passes. The wire of the coil is ex- 
ceedingly thin, and the apparatus is so delicately made, balanced, 
and journaled that it operates under the effect of an almost infin- 
itesimal current. 

The elements of the Deprez-D'Arsonval galvanometer embodied 
in a portable instrument constitute the essential parts of the 
voltmeter generally adopted in American practice. The field is 
established by permanent magnets, with a circular opening be- 
tween the poles for the coil to rotate in. Within the coil, and 
concentric with it and with the cylindrical opening, is a cylinder 

458 



VOLTMETERS AND AMMETERS. 



459 



of iron, which operates to reduce the air gap, thereby intensifying 
the magnet field. The iron cylinder is fixed in position. This 
leaves an annular or ring-shaped opening between the core and 
the pole pieces, unobstructed except where the support of the 
core comes. This only takes up a few degrees of the circle. The 
coil turns in this space. In Fig. 330, SS and NN indicate the field 
poles, PPthe pole pieces, and the cylindrical core is shown be- 
tween them. The coil is also indicated. It moves freely in the 
space between core and pole pieces, touching neither. There is 
no difficulty with the core support, because the coil never turns 
through a full half-circle, and therefore never touches the sup- 
port. To understand clearly the 
relations of core coil and pole 
pieces. Fig. 468 on page 611 may 
be referred to. This shows the 
Deprez-D'Arsonval galvanometer, 
in which the same system of 
field, stationary core, and re- 
volving coil is used that appears 
in the type of voltmeters de- 
scribed here. 

In old practice the voltmeter 
was a high-resistance galvanom- 
eter with a compass needle actu- 
ated by the earth's field and by the coils of the instrument. Such 
a galvanometer had to be placed horizontally with its needle in 
the magnetic meridian when no current was passing. The mod- 
ern instrument is independent of the earth's field, so that it can 
be set up without regard to the points of the compass, and ver- 
tically or at an angle. 

Weston's Voltmeter. — This instrument is very extensively 
used. Its moving part is a small rectangular coil of wire car- 
ried on a shaft whose ends are supported by jeweled bearings. 
To the ends of the shaft are attached the inner ends of spiral 
springs, exactly like the balance or hair spring of a watch. The 
ends are insulated from the axle to which they are attached, and 
one end of the coil wire is connected to the inner end of one 
spring and the other end to the inner end of the other spring. 




Fig. 330.— Field of the Weston 
Voltmeter. 



460 



ELECTRICIANS' HANDY BOOK. 



These connections are electrical, and the springs serve to conduct 
the current to the little coil without preventing it from rotating 
as the current passes through it. They are leading-in springs, in 
the sense that the platinum wires in an incandescent lamp are 
leading-in wires. 

If a balance wheel of a watch were replaced by the coil and 
two hair springs were attached to the axis, one at its top and one 
at its bottom, it would give the mechanical combination of the 
apparatus. It is shown in Fig. 331. 
.The field is that of a horseshoe magnet strengthened by a cyl- 
inder of iron held within the 
coil and concentric with it as 
regards its axis of rotation. 
The cylinder is carried by 
an arm extending from the 
base or frame of the instru- 
ment. It is so placed as not 
to interfere with the swings 
or partial rotations of the 
coil. 

The instrument has a long 
index whose end moves over 
a graduated scale, the arc of 
a circle, and divided into di- 
visions representing and 
calibrated for volts. The 
soft-iron core and the shape 
of the pole pieces secure a uniform field and tend to give a uni- 
form motion for increase of current in the working coil. 

Damping Coil. — To render the instrument "dead-beat," which 
means that it shall at once give its reading without having its 
needle swing back and forth a number of times before coming 
to rest over the proper mark on the scale, a special damping coil 
is used. This consists of a coil of insulated wire short-circuited 
on itself. Over this is wound the active winding, which consists 
of a number of turns of fine copper wire, whose ends connect with 
the springs. This double coil is mounted in the field, and its sides 
move through the annular space between the soft-iron fixed core 




Fig. 331.— Core, Coil, Field 

Poles and Leading-in Springs of 

Weston's Galvanometer. 



i 



VOLTMETERS AND AMMETERS. 



461 



and the magnet poles. As it moves under the influence of a cur- 
rent passing through its active coil, eddy currents are induced in 
the closed circuit of the damping coil, and these oppose its motion 
and thus prevent swinging back and forth. The instrument goes 
at once to its proper reading, and shows the voltage at once. 

Air=Vane Damping.— An aluminium vane is sometimes attached 
to the index. As the latter moves, it sweeps the vane through the 
air. The resistance of the air operates to mechanically damp 
the movements of the index, and to make it still more aperiodic. 




Fig. 332.— Plan of the Empire Voltmeter, 



The critical point about calibrated instruments of this type 
is to secure a permanent and unchanging magnetic field. This 
depends on the permanent magnets retaining their magnetism 
unchanged, year after year. To secure this feature, they must 
be made of a proper quality of steel. Much secrecy is observed 
as to this point. They also are not magnetized to saturation; 
about three-quarters saturation is good practice. 

Empire Voltmeters. — The cuts. Figs. 332 and 333, show the con- 
struction of the Empire voltmeter. Its general construction re- 
calls the D'Arsonval instrument more than does that of the Wes- 
ton voltmeter. The characteristic feature is that the needle is 



462 



ELECTRICIANS' HANDY BOOK. 



carried by straight phosplior- bronze wires kept strained by- 
spiral springs. These wires by their torsion act to keep the coil 
in a neutral position, and to bring it back to zero if it is turned 
away from it. They are also the leading-in wires for the cur- 
rent. 




Fig. 333.— The Empire Voltmeter. 



From the inner surface of the field-magnet poles four flat plates 
of iron project. These form a strong field, made still stronger by 
a disk-shaped core supported between them. The coil includes 
the disk within its open center, but touches no part of the field. 
The suspension wires, which are also the leading-in wires, as 
stated above, are kept strained by springs contained in little 
tubes at the opposite ends of the support. Standards attached to 



VOLTMETERS AND AMMETERS. 463 

the four pole pieces carry cross pieces, to wliich the spring sup- 
ports of the suspension wires are attached. The connections of 
the instrument are omitted in the diagram, which is designed to 
show the characteristic features only. 

Graduation of Voltmeter Scales. — The instrument is put in 
parallel with a standardized voltmeter, and the value of its full 
reading is noted. This may read widely different from the 
truth. Suppose the scale is to be graduated to 150 volts, and 
that 30 volts bring the needle to the end of the scale as yet un- 
marked. At this point a mark is made. The potential is now 
lowered to 28 volts, and another mark is made, then to 26 volts, 
and so on. This gives fifteen divisions on the scale. Bach di- 
vision is evenly divided into ten divisions, thus giving 150 di- 
visions. The 150 divisions correspond to 30 volts. Resistance in 
series with the coil is now placed in the interior of the case, in 
the shape of spools of fine insulated wire. It is tested and added 
to or reduced until a potential of 150 volts carries the index ex- 
actly to the end of the scale. The instrument is then standardized 
and ready for use. 

General Notes on Voltmeters,: — The index is counterpoised so 
as to be perfectly balanced. Its one end forms the pointer. Its 
other end, prolonged beyond the suspension axis, sometimes has 
a thread cut upon its end, on which counterpoise nuts are screwed 
back and forth to secure perfect balance. Sometimes this end of 
the index is bent at right angles, and has counterpoise nuts on 
the bent portion as well as on the straight portion, to give greater 
power of securing a perfect balance. 

To secure an approximately even motion of the pointer, so 
that a given change of voltage shall cause the pointer to move over 
the same number of degrees at all parts of the scale, the com- 
bined effect of the even magnetic field and of the springs is 
relied on. 

Cardew Voltmeter. — This instrument, which would seem pecu- 
liarly well adapted for alternating currents, is not as much used 
as is Siemens's dynamometer. It is really an ammeter of very 
high resistance. Its action depends upon the expansion of a wire 
through which a current passes. This wire expands with heat 
and contracts with reduction of temperature, and the temperature 



464 E^LECTRICIANS' HANDY BOOK. 

'changes depend on the current passing through it. Thes>e 
changes depend on the changes in voltage at its terminals, and 
it is a voltmeter in practice. 

In its essentials a wire is attached to a rotating shaft which 
carries an index. The other end of the wire is attached to a point 
a foot or more distant from the shaft, and is stretched. As it 
changes in length, it turns the shaft. The latter is provided with 
an index, which indicates the changes in length of the wire. The 
simplest construction has a straight wire stretched through the 
center of a brass tube. 

It has to be calibrated by trial for various electromotive forces. 
After enough readings for definite values have been found, others 
may be intercalated between them. If calibrated for continuous 
electromotive force, its readings for alternating electromotive 
force will give the effective value. 

Its sensitiveness is greatly increased by using a longer wire. 
To keep the size of the instrument within practical limits, the 
long wire is carried back and forth over pulleys made of bone. 

In a recent example, the wire of platinum-silver alloy was 0.0025 
inch in diameter and 13 feet long. It passed up and down eight 
times. This brought each stretch of it to a length of about 18 
inches. The terminals of the instrument connect with the ends 
of the wire. When connected to the circuit whose voltage is to 
be measured, the thin wire very quickly acquires the full temper- 
ature due to the current produced by the voltage. The thinness 
of the wire enabling it to grow hot or cold with great rapidity 
makes it very quick-reading, or almost dead-beat. Such an in- 
strument can measure voltages from 30 to 120 volts. For higher 
voltages a resistance is added. This is sometimes made of ex- 
actly the same wire and stretched through metal tubes, as in the 
instrument itself. 

There is considerable vagueness in the readings near the zero 
point, and it is considered inaccurate in the upper part of the 
scale. 

In the construction shown in Fig. 334 a long wire C, carried 
up and down a frame four times, is used. The current passes 
through this, and its changes in length draw the little pulley at 
its upper central bend or bight up and down. By wheel mechan- 



VOLTMETERS AND AMMETERS. 



465 



ism these movements cause an index like a clock-hand to re-* 
volve on a dial, which in the cut is facing away from the reader. 
A pulley P, around which the wire passes and to which it is se- 




FiG. 334.— Cardew Voltmeter. 

cured, turns clockwise as the wire lengthens and vice versa. 
This pulley actuates the index. The spring S drags the pulley 
around clockwise; the contracting wire drags it the other way. 
A larger view of the pulley P is given, to show how the wires are 
attached to it. The index and scale are omitted from the cut. 



J 



466 



ELECTRICIANS' HANDY BOOK. 



Hot=Wire Instruments. — The Cardew voltmeter is the parent 
of the hot-wire instruments. It has tended to go out of use of 
late years. It is affected by alternating as well as by direct cur- 
rents, and this operated to keep it in use. Hot-wire instruments 
have had quite extensive application and are still in use. 

The Stanley Hot=Wire Voltmeter.— A wire is secured across 




Fig. 335 —The Stanley Hot- Wire Voltmeter. 



the upper part of the instrument, and is held horizontally in 
general position. Two leading-in springs or connections descend 
from above and carry current to it, so that the current passes 
through the few inches of wire between the ends of the leading- 
in connections. From the center of this actuating wire another 
wire descends to the bottom of the instrument, and is secured 
there. This wire is approximately at right angles to the actu- 
ating wire. To the left of its center is the index with horizontal 
axle, carrying a pulley or drum fixed to it, A filament from the 



VOLTMETERS AND AMMETERS. 



467 



center of the vertical wire passes around this drum, and has its 
other end secured to a spring. Thus this spring keeps the sys- 
tem of filament, vertical wire, and actuating wire in tension. A 
current passed through the actuating wire heats it and causes it 
to expand. A very slight expansion causes its center to descend 
a measurable distance, on the elbow-joint principle. This magni- 
fication of motion is repeated by the vertical wire, so that an 
infinitesimal change in length of "the actuating wire by means of 
the two magnifications causes the index to move a visible dis- 
tance. 




Pig. 336.— The Stanley Hot- Wire Voltmeter, 



The cuts, Fig. 335 and 336, give the general view of the working 
parts of the instrument. 

The hot-wire instrument is unaffected by any electro-magnetic 
fields, and hence is peculiarly well adapted for places where such 
fields exist. 

Ammeters.— The word ammeter is an abbreviation for ampere- 
meter. It is an apparatus for measuring current rate. Any cali- 
brated galvanometer with its scale marked so as to read amperes 
is an ammeter. 

Total-Current Solenoid Ammeter.— The first instruments were 
constructed so that the entire current passed through the actu- 
ating coils. The cut. Fig. 337, shows a modern total-current in- 
strument. A coil of heavy wire is secured to the base of the in- 



468 



ELECTRICIANS' HANDY BOOK. 



strument. Its axis is vertical. Through its center a core of 
iron is free to play up and down, being suspended from the end 




JPiG. 337.— General. Electric Company's Total Current 
OR Solenoid Ammeter. 

of a bent lever. The latter has one end prolonged to form the 
index. As more current passes, the core is drawn downward, 
and the needle moves over the scale in one direction. If the cur- 




FiG. 837a.— Ammetfr Connec 
TioN WITH Shunt. 



Ammeter Shunt. 



rent diminishes, the core rises and the needle moves the other 
way. Although such an instrument may work with total cur- 
rent, it may be connected in shunt with a conductor, so that 



VOLTMETERS AND AMMETERS. 469 

only part of the current will pass through it. In this way it 



^ 




Fig. 339,— Transformer fob Stanley Hot Wire Ammeter. 



can measure a much larger current than its coil could carry. 

The coil attracting a 

plunger is called not 

quite correctly a sole- 
noid. 

Shunted Ammeter.— 
This instrument is a 
shunted galvanometer, 
which is calibrated to 
read amperes. The am- 
peres are those which go 
through the shunt and 
actuating coils. The 
indicating portion of 
the apparatus is identi- 
cal with a voltmeter. A 
heavy shunt sufficient in 
carrying capacity for 
the full current is con- 
nected in parallel with 
it, and the calibration 
is made to fit these con- 
ditions. The resist- 
ance of the shunt is very low compared 




Fig. 340. 



Alternating Current Volt- 
meter Compensator. 

to that of the instru- 



470 ELECTRICIANS' HANDY BOOK. 

ment. The diagram of the connection is given in Fig. 337a. 
Various forms of shunt are employed, one of which is shown in 
Fig. 338. 

Transformer Ammeter. — Sometimes on alternating current 
work a transformer is used to take off current for a voltmeter. 
By properly proportioning the coils and instrument the voltmeter 
becomes an ammeter. Fig. 339 shows a transformer mounted on 
a bus-bar which forms its primary. The terminals from the sec- 
ondary go to a Stanley hot-wire ammeter. The whole is so cali- 
brated that the readings of the instrument give the amperes pass- 
ing through the bus-bar. 

Wattmeter. — A modification of the construction of the volt- 
meter gives a wattmeter. In this instrument there are two ac- 
tive colls. One is fixed and the other is movable. The fixed coil 
increases the field in which the other one moves, and the index 
readings are a product of the voltage and am^perage of the circuit. 
This multiplying action is in line with the action of magnet poles 
on each other, tho intensity of which is the product of the two 
intensities, and not the sum. 

Pressure Lines or Pilot Wires. — Sometimes small conductors 
are run to various points in the district, are tapped into the 
system, and their ends in the station are connected to the ter- 
minals of voltmeters. These voltmeters give the potential differ- 
ence at the distant points to which their wires lead, and the read- 
ings of the voltmeters are the factors for operating the machinery 
in the station. 

Compensated Voltmeter. — A voltmeter wound so that its read- 
ings practically solve Ohm's law is sometimes employed, con- 
nected directly to the mains in the station. 

It is a voltmeter containing an auxiliary coil wound in opposi- 
tion to the main coil. This auxiliary coil is proportioned to the 
main coil as the feeder drop is to the total potential difference. 
Such an instrument gives pretty closely the potential difference 
at the end of the feeder. 

Compensators.— A compensator is an instrument for use on al- 
ternating-current circuits which indicates voltage between dis- 
tant points of a circuit. The compensator is installed in the 
station, it may be a mile or more from the place to which its in- 



VOLTMETERS AND AMMETERS. 471 

dications apply. In constant-potential lighting, for which it is 
specially applicable, pilot wires are sometimes used to give con- 
nections for voltage determinations at distant points. Such 
wires are connected to any desired point on the circuit, are led 
into the station and there connected to a voltmeter. The readings 
of the instrument give the potential difference or voltage at the 
more or less distant point on the circuit from which the wires 
come and to which they are connected. The compensator gives 
the same voltage reading without the use of pilot wires. 

The Ohmic Compensator includes a transformer whose pri- 
mary is connected in series with the supply line. The active 
turns of the primary can be varied by a switch, with a number 
of contact studs, each one corresponding to and throwing into 
action a greater or less number of turns in the primary. The 
secondary, also adjustable, connects with a voltmeter. This con- 
nection may be a simple series connection, but sometimes it is 
connected to an auxiliary coil, which is wound around the volt- 
meter-actuating coil. This coil is so wound or connected that it 
opposes the action of the voltmeter coil. The action is like that 
of the series coil on a compound-wound dynamo. The action of 
the auxiliary coil increases with the current which passes through 
the main conductor. This increase of current fndicates the need 
of higher voltage, and to make the voltmeter read the same, the 
voltage of the circuit has to be increased to make its own proper 
coil pull harder against the auxiliary coil. Thus, if the voltmeter 
is kept at a constant figure, more voltage must be given to the 
line as more current is given it. 

By adjustment with the switch and contact plugs the readings 
of the voltmeter can be made to correspond with any desired drop 
on the line per given intensity of current. 

The Inductance Compensator has a second switch with a num- 
ber of contact plugs, by which the adjustment for inductance on 
the line is made, so that the total impedance is taken into account. 
The instrument is shown in Fig. 340. 

A compensator is without action of any appreciable degree 
upon the circuit. Its action on the voltmeter is such that in 
order to maintain a constant reading of the voltmeter, the pres- 
sure on the circuit must be increased as the current increases. 



CHAPTER XXVIII. 

DISTRIBUTION. 

Two Distribution Systems. — The systems of distribution of 
electric power may be divided into two main divisions — the con- 
stant-current and the constant-potential systems. In the constant- 
current system the central generators force an unvarying current 
through the circuit. The potential of the dynamos must rise 
and fall as the resistance of the circuit varies under different 
conditions, but the same number of amperes must pass over the 
line. In the constant-potential system the generators are oper- 
ated to keep a constant average voltage between the two leads 
of the circuit; the amperage may vary from almost nothing up 
to very high values; the station voltage may rise a little in its 
readings as more current is taken, and may fall a little as less cur- 
rent is taken. These variations compensate for the distance from 
station to district. 

Arc and Incandescent Lamp Circuits.— Lamps and motors are 
the principal appliances for utilizing electric power. All lamps 
require a constant current. Arc lamps without individual re- 
sistances or reactances can only be operated on constant-current 
systems. By the use of these individual attachments, which are 
described later, arc lamps are used on constant-potential sys- 
tems in very large number. Incandescent lamps can be used on 
either constant-current or constant-potential system. Motors can 
be connected so as to work on either system. 

Constant- Current Systems. — A constant-current circuit con- 
sists of two leads carried through the district to be supplied. 
The leads are without branches or deviations properly so called; 
they unite at the most distant part, and form a simple closed me- 

472 



DISTRIBUTION. 



473 



tallic circuit. Lamps to be lighted are placed in their circuit, so 
that the entire current from the station goes through every 
lamp, and every lamp gets the same current. 

The potential on a constant-current system may vary consid- 
erably. A lamp may be removed from the line, and the ends of 
the line may be directly connected without resistance being in- 
serted in place of the lamp. In such case the potential of the 
lamp will be taken out of the system, and the generators will 
have to be run at a potential lower than the original potential 
by an amount equal to that of the lamp taken out. The amperage 
will be the same as before the removal of the lamp. 

The constant-current system is also called the series system; 
it supplies power by se- 
ries distribution. It is 
shown in diagram in Fig. 
341. 

Constant = Potential 
Systems. — The two-wire 
constant-potjential system 
begins with two leads, 
^hich may divide into 
any number of branches, 
each branch consisting 

of two parallel leads, one from each original lead, and the two 
leads are not united at their ends, but are on open circuit, ex- 
cept as closed by the lamps or other appliances. 

The three and other multiple wire systems do the same, except 
that instead of two parallel lines three or more as the case may 
be are carried through the district, branching whenever it is 
necessary and always on open circuit except for the lamps or 
other appliances. 

The constant-potential system operates by parallel distribution. 
The lamps or other appliances used are sometimes said to bear 
to the main leads the relation of the rungs of a ladder to its sides. 
It is shown in Fig. 342. 

Series Distribution. — In series distribution of electric energy 
the lamps or other appliances to be supplied with current are 
placed in series with each other. The illustration, Fig. 341, 




Fig. 341.— Constant Curbent Distribtttion. 



474 ELECTRICIANS' HANDY BOOK. 

shows a diagram of series distribution to a number of lamps. 
The simplicity of the system is obvious. A wire circuit, whose 
capacity for current is equal to that of a single lamp, can sup- 
ply any number. There is no question of increasing the size 
of the wire as more lamps are put into service. In these respects 
its advantage over the constant-potential circuit is very great. 
With one exception its limitations are not very great. 

Limitations. — One limitation is that each lamp must be con- 
structed for the same current. The potential drop for each one 
would normally be the same, but this is quite unnecessary. An- 
other limitation is that the total potential difference existing be- 




Fig. 34S. Constant PoTENTiAii Distribution. 

tween the ends of the line shall not be too great. This is a prac- 
tical consideration affecting safety to life and possibility of in- 
sulating adequately. 

The next limitation to be noticed is one which has relegated 
series lighting to a very limited field. It is not practicable to put 
out one light without substituting for it some equivalent resist- 
ance or inductance. The latter can only be used for alternating- 
current systems, and high-voltage alternating-current systems are 
not supposed to have single lamps extinguished by hand, on ac- 
count of danger to life. 

It follows that domestic illumination cannot be organized on 
the lines of series system of distribution, because single lamps 
cannot be extinguished. It is not practicable to supply every 



DISTRIBUTION. 475 

lamp in an incandescent lighting circuit with a resistance equal 
to its own, to be substituted for it when extinguished. If prac- 
ticable, it would be uneconomical. 

Features of Series or Constant^Current System for Arc 
Lamps.— It will be evident that as every lamp receives the same 
current, the wire should be of one size throughout. It is also 
evident that were there one or a hundred lamps on the circuit, 
the same current would pass and the same sized wire would be 
required. It follows that the economy in wire is increased by 
placing as many lamps as possible on the one circuit. 

The simplicity of the system is seen in the cut. A single line 
runs out from the generator and returns to it with as many 
lamps put on it as the voltage of the machine can take care of. 
There are no real branches or other complications. 

The management is also of the simplest. The dynamo is to be 
made to supply a constant current and to give the potential re- 
quired to keep up the current strength. 

Fifty to one hundred arc lamps may be placed on one circuit, 
which may be several miles in length. An ordinary arc lamp 
would require ten amperes of current and would develop a poten- 
tial drop of fifty volts. 

Calculations. — The calculation for a plain series distribution is 
simplicity itself. Take as an example fifty arc lamps, each of 

tf> 
10 amperes and 50 volts. By Ohm's law, R =_, the resistance 

of one such lamp would be 5 ohms. There is a total drop in the 
lamps of 50 (volts) X 50 (lamps) or 2,500 volts to be provided for. 
Besides this, a current of 10 amperes has to be forced through the 
line. Take one mile as the length of the line, and assume that 
a loss of 5 per cent of the lamp energy on the line is admissible. 
As the current is a fixed quantity, the watts of energy are pro- 
portional to the resistance, because IE (watts) = R I^ The re- 
sistance of the lamps would be 5 (ohms) X 50 (lamps) = 250 
ohms. Five per cent of 250 ohms is 12.5 ohms. 

Consulting a wiring table, we find that No. 14 wire would give 
a resistance per mile at ordinary temperatures of 13.31 ohms, 
and No. 13 wire would give a resistance of 10 6 ohms. 

If we wished to have an exact resistance of 12.5 ohms, we could 



476 ELECTRICIANS' HANDY BOOK. 

use both sizes of wire in the line. Calling x the relative length 
of No. 14 wire required, 1 — x will be the relative length of No. 
13 wire required. Multiplying the relative length of each wire by 
its resistance per unit of length, we have the equation 

13.3iP + 10.6 (1 — X) = 12.5, 
which being solved gives: 

X = 0.7 for No. 14 wire and 1 — a? = 0.3 for No. 13 wire. 
Multiplying each factor by its resistance, we have 
0.7 X 13.3 = 9.31 No. 14. 
0.3 X 10.6 = 3.18 No. 13. 



12.49 
The decimals 0.7 and 0.3 refer to a unit of 1 mile, and multiply- 
ing 5,280 feet (the feet in one mile) by them, we have: 
8,696 feet of No. 14 wire. 
1,584 feet of No. 13 wire. 

5,280 feet or 1 mile. 
But it would be unnecessary to work so close as this. Mech- 
anical considerations apply also under the head of good practice. 
No. 8 wire is the smallest that is approved on arc-light circuits. 
If the mile of wire were of this size, its resistance would be about 
3.3 ohms. This would bring the energy absorbed by the line to 

Q Q 

== .0132, or 1.3 per cent of the lamp energy. 



X 50 

Where the percentage is so small, this would be almost exactly 
the percentage if the total energy of line and lamps together 
were taken as 100. 

Keeping in mind the law that resistance is to be concentrated 
in the appliances in which heat or light energy is to be devel- 
oped, the object of keeping the line resistance low is to avoid 
waste of power on the line. 

Advantage of High Potential. — In the early days of electric 
lighting, a number of deaths occurred from contact with arc-light 
circuits. The higher potentials involve the greater danger. High po- 
tential of a circuit makes the adequate insulation more difficult than 
it is for the lower voltages. The idea is that it is good practice to 
keep voltage as low as is consistent with economical installation. 
In general terms, the high voltages are more economical in the 



DISTRIBUTION. 477 

wire required for the distribution of electric energy. The unit of 
rate of energy is the volt-ampere or watt. With high voltage the 
amperes for a given number of volt-amperes will be less than 
with a low voltage. Thus 100 volts multiplied by 100 amperes 
gives 10,000 volt-amperes or watts of power, which is also given 
by 1,000 volts multiplied by 10 amperes. But the larger number 
of amperes need a larger conductor than do the small number. 
Increasing the voltage and decreasing the amperage saves capital 
invested in lines. 

Standard Series Lighting Current. — For arc lighting on the 
series system a sort of standard has been established in the 10- 
ampere current. A station supplying circuits of this type simply 
has to send out 10-ampere currents, and as long as they pass to 
the line, the engineer can be almost certain that all is well in the 
district. The voltmeter will indicate the extinction of a lamp on 
the circuit. 

Series Incandescent Lighting. — What has been said about arc 
lighting applies to series incandescent lighting. The lamps are 
made of dimensions adapted to the current. If the arc-light cur- 
rent of 19 amperes is used, the incandescent lamps must have 
very thick filaments of length adapted to establish a relatively 
low potential difference. Thus, were it proposed to put one hun- 
dred ordinary incandescent lamps on one circuit in series, the 
potential difference due to them alone would be over 11,000 volts, 
and only one-half ampere of current would be required. One 
hundred thick and short filament lamps, on the other hand, would 
replace about double the number of arc lamps and would work 
with the same current and potential difference. 

An incandescent lamp for this work passing 10 amperes of cur- 
rent by the expenditure of 10 volts would give at 3 to 4 watts to 
the candle power about 32 candle illumination. About thirty 
such lamps would give the light of a single arc lamp of 10 am- 
peres and 40 to 50 volts. The economy is poor, but is offset by other 
considerations, one of which is the evenness of distribution. A 
large number of small lamps give a more even light than that 
afforded by a few more powerful lamps. 

For outdoor lighting a 10-ampere, 100 candle-power lamp is a 
standard. 



478 



ELECTRICIANS' HANDY BOOK. 



Film Cut=Out. — In all the series systems the entire electromo- 
tive force of the circuit would appear if the circuit were broken. 
This applies to the three-loop Brush system as much as to any 
other. This gives a simple method for constructing a cut-out 
whicli' will short-circuit a broken lamp through which no cur- 
rent can pass. It is called the film cut-out. 

The ends of the line connected to the lamp are bifurcated, as 
shown in Fig. 343. Between the free ends a piece of paper or 
other film is interposed, the ends pressing against it, thereby 
sending the current through the lamp. But if the lamp breaks or 
the filament parts, the voltage due to the 
entire electromotive force of the system 
is developed on the two ends of the con- 
ductor separated by the film. This is at 
once pierced, the ends of the conductor 
spring together, and the current passes. 
The resistance of the lamp is gone from 
the circuit, so the current has to be re- 
duced from the central station to save the 
lamps from overheating, with consequent 
breaking down. 

Relief Lamps. — On each circuit in the 
station one or more idle or relief lamps 
are provided. The attendant watching the 
ammeters recognizes the breakage and 
cutting out of a lamp by the increase of current on the line con- 
taining it. He then throws one of the relief lamps into the cir- 
cuit. This reduces the current to the normal, and the broken 
lamp has to be dispensed with until replaced. 

The relief lamp is one of many cases in electric engineering 
where a lamp is used as a resistance. As a lamp sooner or later 
burns out, it is an expensive resistance. It has one good side, 
however. The bright lamp shows that something is wrong. A 
common resistance would disclose nothing except by the position 
of its switch. 

nultiple=Series System. — Incandescent lamps for street light- 
ing are sometimes made for a lower current, 3 to 3.5 amperes. 
To enable a larger current to be used, several series of such 




Fig. 343.— Film Cut-Out. 



DISTRIBUTION. 



479 



lamps may be placed in parallel with each other, as shown in 
Fig. 344. Each series must be of the same resistance, or it will 
not receive the proper current. This is termed the multiple-series 
system. As the same number of lamps are on each circuit, it fol- 
lows that if the lines connecting them are of identical resistance, 
the circuit can be operated on constant potential. The property 
possessed by some makes of incandescent lamps of increasing in 
resistance as they rise in temperature operates in multiple-series 
distribution to even the currents received in the parallel lines of 
lamps. This self-regulating quality works in one way disadvan- 
tageously. A very slight rise in voltage makes the lamp work 
at an exceedingly great economy in consumption of electric en- 
ergy, but a slight fall dims the light very badly. 




Fig. 344.— Mcltiple Series. 



This feature may to some extent provide for the contingency 
of a lamp breaking down and being automatically short-circuited. 
The potential drop in that series is distributed among less than 
the proper number of lamps, and they burn too brightly, but not 
to such an extent as if their resistance was unaffected by heat. 
But incandescent lamps as a rule are made without this self- 
regulating quality. 

•♦Municipal** Series Incandescent Lighting is often carried out 
on these lines, lamps using 3 to 3^,^ amperes being employed. 
Thus with a 10-ampere machine three series could be operated in 
parallel. 

Series -Multiple System,— Another system of distribution for 
incandescent light is termed series-multiple. In it the lamps are 
put in parallel in groups, and any number of these groups ac- 
cording to the potential available are put in series. The cut. Fig. 



480 



ELECTRICIAN&' HANDY BOOK. 



345, shows the arrangement. By selecting lamps of suitable 
voltage and grouping them in parallel, each group can \)e made 
to represent any resistance equivalent to or calling for any current 
desired. All the lamps in one set must agree in voltage rating — ■ 
all the station is called upon to give is a constant current of known 
amount, and the voltage must be enough to produce this current. 
It is possible to introduce lamps of different candle-power in 
this system, provided (a) that they are of the same voltage as 
the others and (&) that the current required for each group of 
lamps is the same. Thus a group could be composed of five 16- 
candle-power 50-volt lamps or of three 16-candle-power 50-volt 




Fig. 345.— Series-Multiple Connection. 



lamps and of one 32-candle-power 50-volt lamp. Many variations 
can be made in a group, provided the requirements as outlined 
are fulfilled. 

If one of the lamps breaks down, it will cause the entire group 
of which it is a part to receive too much current, and will tend 
to burn out the lamps. This can only be met by having an auto- 
matic device of some kind which will switch in a new lamp in 
place of the other, or which will cut out the whole group. In 
the latter case the voltage of the system will be suddenly re- 
duced. The station must take care of this, and maintain a con- 
stant current or all the lamps will receive too much current and 
be in danger of burning out. 

This system is very little used. The difficulties to be overcome 
in providing for the contingency of lamps breaking down militate 
against it. 



DISTRIBUTION, 481 

Objections to Series Distribution. — Series distribution for in- 
candescent lighting involves several features that militate 
against its use in houses. It requires too high a potential. A 
high-potential system is a cause of danger to life and property. 
It exacts that a number of lamps be operated as a unit. A single 
lamp cannot be turned on and off without disturbing the whole of 
its group, unless an equivalent resistance or inductance for alter- 
nating circuits be substituted. A resistance for every lamp 
would involve expense in installation, and would absorb just as 
much energy as a lamp and make no return. An inductance ab- 
sorbs but little energy and is an important adjunct in outdoor 
circuit work in alternating-current lighting. But the great dan- 
ger of a considerable voltage on an alternating-current system 
absolutely proscribes indoor alternating-current series lighting. 

Parallel Distribution is constant-potential distribution. In 
parallel lighting pairs of mains or wires from the electric station 
are kept by the station machinery at a constant difference of po- 
tential. The lamps are arranged in parallel across them, as has 
been said, like the rungs of a ladder, as far as their representa- 
tion in a diagram is considered. Incandescent lamps are con- 
structed for a specific current by being made of adequate thick- 
ness of filament and of length sufficient to operate at the de- 
sired current with a specified drop of potential. One hundred and 
ten volts is a sort of standard. For half an ampere of current, 
the filament has to be of two hundred and twenty ohms resist- 
ance. Lamps are made, however, of the most various voltages, 
and are generally rated by the voltage required to operate them. 

If for 110-volt lamps the mains are kept at a constant difference 
of potential of 110 volts, perfect independence of action of all the 
lamps is established. They may be lighted or turned off one by 
one without affecting each other to any noticeable extent. The 
maximum difference of potential in two-wire circuits is that of a 
single lamp, which cannot hurt anyone and is treated as a safe 
potential as far as fire risks are concerned. The electric energy 
of the system is drawn upon in almost exact proportion to the 
number of lamps lighted. 

The conditions of safety, simplicity, and economy of energy are 
adequately fulfilled by the parallel circuit. 



482 ELECTRICIANS' HANDY BOOK. 

Disadvantages of Parallel Distribution. — On series connec- 
tion one hundred lamps could be supplied with current through a 
wire of one-hundredth the cross section of that required for cur- 
rent for the same lamps in parallel. This is a most important ad- 
vantage. Heavy currents in electric engineering involve expense 
of installation at every part, and the interest on the capital in- 
vested is to be treated as a part of the fixed charges of the sys- 
tem. The independence of each lamp of the circuit has made the 
parallel lighting system universal for indoor illumination. Where 
the street mains already exist, it is used for arc lighting with the 
attendant sacrifice of economy involved in the use of an individual 
resistance for each lamp. 

Elementary Case of Parallel System, — The simplest case is 
shown in the cut. Fig. 342, where two leads of even thickness are 
CfiTried out through the district, and have as many lamps con- 
nected across them as they can carry current for. This is waste- 
ful of copper, because the wire which comes between the first 
lamp and the dynamo determines the size of the outer end of the 
wire. Current for all the lamps has to go through the wire next 
the dynamo, while at the outer end current for only one lamp is 
to be carried, and it is wasteful of copper to use too large a con- 
ductor. 

The size of a conductor is determined by several considerations. 
It must carry the current without undue heating. It must be of 
low enough resistance to pass the current at a low enough drop 
to secure economical working. The latter consideration is the 
controlling one, as under its requirements the wire is sure to 
be large enough to carry the current with safety from overheating. 

Potential Drop in Parallel System. — Incandescent lamps for 
a variation of one per cent down or up in potential drop lose or 
gain a little over one-sixteenth of their illuminating power. A 
drop of one volt in a 110-volt 16-candle-power lamp will reduce 
its candle-power to 15 candles. The consumer's payment is based 
on light and only indirectly on electric energy. A drop in voltage 
deprives the customer of the light he is paying for, and the re- 
duction in fuel consumption due thereto is too trifling to be con- 
sidered. It amounts to failure in carrying out a contract and to 
injury of the customer without benefiting anyone. The utmost 



DISTRIBUTION. 483 

care should be taken in planning a system to obtain good dis- 
tribution of potential. Inevitable variations in potential drop 
can be allowed for by using lamps of different voltage. But after 
all calculations are made, the results in practice will vary, be- 
cause various numbers of the lamps may be lighted at once. The 
calculations have to refer always to all the lamps or to some 
fraction of their total. Their results will not stand for any other 
number. 

Feeders, flain and Leads. — Districts are not supplied by a sin- 
gle pair of conductors. Feeders run out from the station to points 
in the district, and are not supposed to be tapped for lamps. 
These are and should be of uniform thickness. Their ends connect 
with other wires, called mains. Between the ends of the first lines 



i i i i 



Fig. 346.— Loop System. 

of feeders and the lighting mains secondary feeders may inter- 
vene. By tertiary and other feeders the system may be made 
quite complicated. From the mains run other wires called leads, 
and the lamps are supplied by them. 

Classification. — The calculations for supplying a district are 
based on Ohm's law, and whatever arrangement of mains and 
feeders is adopted, the calculations are simple. Classification of 
the systems of supply may be elaborate, but they all are subject 
to Ohm's law, worked best perhaps by the drop system of calcula- 
tion. 

Loop System.— The loop system of distribution arranges the 
circuits so that the current for each lamp goes through the same 
length of wire. There are two loop systems shown in the cuts. 
Figs. 346 and 347, the straight loop and the spiral loop. If the 
reader will examine the length of conductor through which the 
current for each lamp passes, he will find that the lengths are 



484 



ELECTRICIANS' HANDY BOOK. 




Fig. 347.— Spiral Loop System. 



identical. With a constant current the line drop for each lamp 

would be the same; for a dimin- 
ished current, due to the extin- 
guishment of some of the lamps, 
the line drop varies. 

The amount of copper required 
for loop system conductors is 
greater than in other systems, but 
the potential is much better main- 
tained than in systems more eco- 
nomical of copper. 
Tree System.— In the early installations a pair of mains was 
carried from the station through the district. From this pair a 
quantity of minor conduct- 
ors were carried to supply 
the lamps. The plan laid 
out in simplified form re- 
sembles a tree, with the sta- 
tion as the root or pot out 
of which it grows. The two 
mains are the trunk and the 
branches, with minor 
branches to carry the lamps. 
The cut, Fig. 348, elucidates 
the origin of the name, the 
"Tree System," given to it. 
Closet System.— Another 
system is the "Closet Sys- 
tem." In it the lamps are 
collected into groups. Bach 
group has its own circuit 
running back to the dyna- 
mos. The method is used in 
interior wiring. An interest- 
ing example is shown in the 
cut, Fig. 349, where two 
feeders are connected to op- 
posite sides of a double circle of mains, across which the lamps 




O Camps 
glLSwitcheB. 
caSafety Cut^Oirttf 



F2G. 348.— Tree System of PARALLBii 
Distribution. 



DISTRIBUTION. 



485 



are connected by their individual leads. In this arrangement 
the length of main for each lamp is identical. This length is 
half the circumference of the 
circle, assuming that the 
lamps are so close to the 
mains that the circles of wire 
virtually coincide. In prac- 
tice this scheme would be 
carried out by two more or 
less irregularly-shaped cir- 
cuits of mains. The feeders 
would be tapped in at opposite 
points. 

In Fig. 350 the closet sys- 
tem is shown as carried out 
for a number of lamps ar- 
ranged in four closet connec- 
tions, with voltmeters and 
fuses for each group. 

Cylindrical and Conical Conductors, — Wire is normally of one 
diameter throughout, and^ is almost always of circular cross sec- 
tion. Where such wire is used throughout a circuit or division of 




Fia. 349.— Closet System op Par- 
allel. Distribution. 




Fig. 350.— Closet System. 



a circuit, the term cylindrical system is applicable. If the wire 
is reduced in diameter as the distance from the station increases. 



486 ELECTRICIANS' HANDY BOOK. 

it represents a cone, and the term "conical" becomes applicable. 
The reduction in diameter may be, and practically always will 
be, by reduction of diameter at various places, so as to constitute 
a step-by-step reduction. The cylindrical system secures the 
most even effects as regards potential difference, while the conical 
system saves copper, and if properly carried out secures good 
enough results in evenness of potential difference. 

It is important to keep in mind the statement of the last para- 
graph; conical distribution. Pig. 351, does not secure even poten- 
tial difference between the lines. What it may secure if properly 
calculated, and if the number of lamps or other appliances as- 
sumed in the calculation are operating, is an even potential drop 
per unit length of line. A drop of this description is simply to be 



n n 



Fig. 351.— Conical Mains. 

accepted as an indicator of good practice and as giving a basis 
for calculating the sizes of conductors. 

Calculation for Conical Conductor. — Assume that lamps to 
be supplied by a main can be divided into three groups for the 
purposes of the calculation. Let the initial difference of poten- 
tial be 115 volts. Suppose the first group of lamps are of an 
average voltage of 114 volts, the next group 112 volts, and the 
last group 110 volts. The wire is to be reduced in two steps. 
"What should be its resistance at the three divisions? Suppose 50 
lamps are in the first group, 60 in the next, and 30 in the last, 
and that each lamp takes % ampere of current. 

. 50 + 60 + 30 
The total current is . .= 70 amperes. By Ohm's law 

■p ■( 

R = and substituting we have R =. — ohm. This is the resist- 

I 70 

ance of the first portion of the mains, or 1/140 ohm for each lead. 



DISTRIBUTION. 487 

to give a drop of one volt for the 114-volt lamps. The next section 

has "" "*" ^ = 45 amperes to supply at a drop of 2 volts; its re- 
2 

sistance is ohm, or 1/45 ohm for each lead. The third has . — . 

45 2 

o 

= 15 amperes at 2 volts, giving a resistance of — — ohm for both 

15 
leads. In diagram the above conditions would be indicated as in 

the cut, Fig. 352. 

Suppose that each section of conductor is of the same length, 
and that it was a cylindrical conductor, one of the same diam- 
eter throughout, and that the diameter was that of its first or 
largest section. The drop for the first group of lamps would be 



A. JL -J- 

140 OHM. 45 OHM. -jf, OHM. 



■ !■■■—■■■ I } 

'flivOLTS 7.a.AMP,. ^114 loLTS > 45 AMP-. -♦.112 |OLTS 15 AMP. 110| VOLTS 

• jr ^140 OHM. i ± I , j 

TLO. 353.— CAIiCDIiATION TOK CONICAL MAIN. 



one volt as before; for the second, by Ohm's law, E = R I, it would 

'he 
30 



be — V — == _^ volt; and for the third Jl X 15 = 1? volt. The 
70 ^ 2 70 70 70 



total drop from the station for the second group would be 1 

70 

volts; for the third group 1 --? -J =z 1 zl volts for the maxi- 

70 ^ 70 70 

mum drop of the system, instead of 5 volts as before. 

The whole question is to be answered for each case partly by 
judgment. This is based partly on the cost of copper per pound 
and the interest charge thereon. As both of these factors vary 
from year to year, there can be nothing decisive about the re- 
sult. The lamps to be supplied and their location are other factors 
also liable to change from time to time, and varying every hour 
in the numbers in use. Very expensive errors have been made 
by assuming that rigid accuracy or even an approach, thereto was 
possible in this class of calculation. 



488 ELECTRICIANS' HANDY BOOK. 

The term cylindrical is convenient as indicating that the con- 
ductor to which it is applied is of even cross-sectional area. A 
great many mains have been used which were not of circular 
cross section, notably in the early Edison installations. The 
term cylindrical can be applied to them to indicate the feature of 
even cross-sectional area. 

Treating the wire of graduated thickness as if it were a true 
cone, it will follow from the laws of geometry that with the 
same initial thickness the conical system will use but one-third 
the copper that the cylindrical one will. This is because the vol- 
ume of a cone is to that of a cylinder as 1 is to 3. The total 
drop in potential in a truly conical system will be twice that on 
the cylindrical one. If the initial section of the conical conductor 
is made three times that of the cylindrical one, it is evident, from 
the proportion stated above, that they will be of equal weight, and 
calculation shows that in such case the drop of the conical con- 
ductors will be two-thirds that of the cylindrical ones. 

A diminution in the total drop is advantageous in two aspects. 
It indicates economy of energy, because less watts are expended 
on the line. It makes the voltage at the place of connection of 
each lamp more even along the line. Lamps of a more even volt- 
age can be used. 

From the above it follows that conical mains are advantageous 
if they are not made of too high resistance. The same weight of 
copper does better work as a conical than as a cylindrical main. 

In practice, conductors are invariably reduced in size as they 
have fewer lamps to supply. Feeders which run out into the dis- 
trict untapped are of uniform size throughout. In electric rail- 
road practice, considerations of strength operate to make the use 
of cylindrical conductors advisable for overhead work. 

Anti==Parallel Systems. — These are systems in which the 
current enters at opposite ends of the two leads of a circuit. 
Thus, one lead will receive current at the point nearest the sta- 
tion, the other at the point most remote. This brings about a 
relatively even potential difference between the two leads, but 
such connection is not always practicable. It is highly advan- 
tageous as compared with the direct connection. The drop takes 
place from both ends toward the middle, 



DISTRIBUTION, 



489 



The diagram, Fig. 553, shows a niimher of lamps or other re- 
ceivers or appliances arranged on the anti-parallel system with 
cylindrical conductors. The characteristic feature of the system 



^ 



M M M 



Fig. 353. -Anti-Parallel System. 



is that no lamp receives the full potential of the system, however 
near the origin of one of the lines. The nearer it is to the origin 



^ 



<- 



Fig. 354.— Anti- Conical DTSTRrBUTiON. 

of one line, the farther it is from that of the other, and thus a 
drop inevitably is introduced. Assuming the lamps to be evenly 



V' i 



C -i — ^ 

Fig. 355.— Anti-Conical Calculation. 



distributed along such a line, the end lamps will have the same 
potential. The greatest drop is in the center of the line. 

Finally we come to conical mains in anti-parallel. The cuts, 
Figs. 354 and 355, indicate the system. On subjecting it to cal- 



490 ELECTRICIANS' HANDY BOOK. 

culation, it appears that when all the lamps or other appliances 
for which it is calculated are in operation, there is no variation 
in the potential supplied to each of them. The figures in Fig. 
355 indicate the relative areas of the conductors. 

All calculations of the systems, it will be understood, were 
made on the supposition that all the lamps, etc., were in oper- 
ation at once. 

Again we have the 3 to 1 ratio of weights of cylindrical and 
anti-cylindrical conductors. If the weights of copper employed 
in a conical and a cylindrical anti-parallel system are the same, 
the conical is far more economical in energy expended on the 
line. 

Individual Voltages of Lamps. — As by calculation variations 
in voltage are inevitably found to exist in different parts of an 
active system, lamps of different voltage are used. A range of 
110 volts to 115 volts may be advantageously employed. The 
low-voltage lamps go to the more distant parts of the system, 
unless, owing to some peculiarities of the circuits, the drop in the 
mains brings the place of low potential near the station. In this 
way the drop in the mains, which increases from generator to the 
outer limits of the district, is compensated for. By Ohm's law in 
its form E = R I the drop of any portion of the main is calcu- 
lated. Its resistance is known as being functions of its length 
and cross-sectional area. The current it has to carry is known 
from the number of lamps it has to supply. On multiplying 
these two factors, the drop for that portion of the main is given. 

If therefore a complete system of electric parallel distribution 
is given to an engineer, he will have, by following out the above 
method, to determine the special voltages of the lamps to be 
placed at different localities. It is quite likely that the system 
may have been laid out with regard to greater consumption 
in the near future. Original calculations based on the full ca- 
pacity of the mains must be discarded, as far as lamp voltages are 
concerned, if only a portion of such capacity is utilized. Calcu- 
lations based on the actual output and on its true distribution 
will give the drops in potential for the various points. Then on 
subtracting these drops from the voltage at the station, the 
proper voltage of the lamps will be found. 



1 



DISTRIBUTION. 491 

This process has, in a growing district, to be repeated from 
time to time as more lamps are put in use. The only final calcu- 
lation is the one covering the district in its final and fixed condi- 
tion. The calculation is accurate only when all the lamps it pro- 
vides for are in use. 

Relation of Current to Drop.— The drop in voltage varies 
with the current intensity. This follows from Ohm's law. The 
current intensity will vary from a very small quantity in the 
daytime to a relatively nigh figure called the "peak," during the 
evening. The drop will on the average vary in like ratio. 
Therefore it is good practice in operating the works to vary the 
voltage in such a way as to take care of the variations in drop. 

Assume the following case: The current supplied by a given 
station at the time of maximum demand is 200 amperes. The drop 
varies from 1 volt to 6 volts at this current, and lamps are dis- 
tributed to suit these figures. At a certain period 100 amperes 
are being delivered. The maximum drop varying with the cur- 
rent will be one-half what it should be, namely, i/^ X 6 = 3 
'volts. The average lamp will receive therefore 3 volts more 
than it should. This condition is met by reducing the initial volt- 
age that much. At another period 170 amperes are being deliv- 
ered, or_lZli_of the maximum current. The drop under these 

conditions is equal to 6 X '- — or a little over 5 volts. 

;iUU ~ 20 

This gives the average lamp 6 — 5 = 1 volt more than it should 
receive. To compensate for this, the station voltage may be re- 
duced this amount. 

This method gives an approximate correction, which may be put 
into a simple tabular form for use in the dynamo room. It is only 
an approximate correction. The saving clause in such cases is 
that the mains in parallel lighting only give a small drop at the 
maximum. But a variation of six volts in an individual lamp 
would be enough to cover the range from the condition facetiously 
indicated as that of a red-hot hairpin to brilliant incandescence. 

The necessity for keeping the maximum drop small makes large 
mains necessary. The drop question is the weak point in incan- 
descent lighting. 



492 



ELECTRICIANS' HANDY BOOK. 



Uniform Potential Hethods. — In some small works the gener- 
ators are run at a uniform potential, one which at full load gives a 
couple of volts or thereabout too little voltage to the lamps, and 
at the minimum or no load gives about the same amount in 
excess. This is a very simple plan, but one not to be imitated. 

If the engineer in charge of the station is of the smallest 
degree of competency, he can run up his voltage as the current in- 
creases so as to follow closely a schedule given him by the 
superintendent. 

Automatic Regulation of Voltage can be obtained in some 
degree by using over-compounded dynamos. A series-wound 
dynamo working on a parallel circuit will increase its voltage as 
each lamp is turned on. A shunt-wound dynamo will lower its 



00 




Fig. 356.— Independent Circuits. 



voltage as each lamp is turned on. It is a simple matter to so 
wind a compound dynamo that as lamp after lamp is turned on, 
its voltage will rise just enough to compensate for the natural 
lowering of the voltage. 

Like some other automatic things in engineering practice, 
this is not as reliable and free from objection as would be de- 
sirable. 

If a short circuit occurs on the line, the voltage will rise just 
as if an equivalent amount of lamps were turned on. But the 
resistance of the short circuit may be so low as to do injury. 
This contingency can be guarded against by the use of automatic 
circuit breakers or safety fuses. 

Independent Circuits are shown in the diagram, Fig. 356. There 
are occasions when such a system may be used. As each circuit 



DISTRIBUTION. 493 

gets the same voltage, th- lamps or motors have to be chosen with 
full recognition of this fact. 

Feeders.— In electric lighting and power circuits on the con- 
stant-potential system, a special class of conductors called feeders 
are employed, whose function is to increase the evenness of the 
potential through the system. 

Feeders are conductors which, starting from the generating 
plant or central station, run out into the district and are there 
connected to the lighting or power mains. No current is sup- 
posed to be taken from them en route. They go out in pairs for 
the two-wire system; for other systems three, five, or seven 
parallel lines are installed. Feeders operate by their direct con- 
nection with the power house to raise the potential of the circuit 
which they are connected to. All of the circuit participates to 
some extent in the increase. The feeder carries current, and there 
is a drop of potential in it also. 

If thore were a given drop in the mains between the power 
station and point of connection of the feeder, it might seem that 
a feeder with a greater drop than this one would be useless. But 
a feeder will always raise potential. It gives a parallel path 
for current, reducing the current in the regular leads, and 
thereby raising potential. The drop in a feeder will never exceed 
that in the mains parallel with it. However small it may be, it 
will improve the service. 

The feeder must not be thought of as delivering station voltage 
to the circuit. Suppose a feeder had a resistance of 0.1 ohm, and 
v/hen connected to a circuit at a distant point delivered 100 
amperes of current at full consumption. Then by Ohm's law 
the drop of potential in the feeder would be E = R I = 0.1 X 
100 = 10 volts. If the station voltage was 125, the feeder would 
deliver 125 — 10 == 115 volts to the circuit. If half the current 
passed through it, its drop would be one-half the above, or 5 volts, 
and it would deliver 125 — 5 or 120 volts to the distant circuit. 

It follows from this that feeders, unless extravagantly large, do 
not dispense with station regulation. They are an adjunct to 
supply circuits, which tends to improve the service. There 
seems no good reason for absolute abstention from tapping them. 
In treating of them they are generally assumed to be feeders 



494 



ELECTRICIANS' HANDY BOOK. 



only, and not to supply energy except to the circuit where con- 
nected. 

Several diagrams of feeder connections are given. In Fig. 
357 a number of feeders, F, F', F", are shown, each with a switch. 




Fig. 357 —Feeders With iNDiviDUAii Switches. 

h, c, or d, by which it can be thrown out of action when de- 
sired. M M are the mains. Sometimes an effort is made to con- 
nect feeders symmetrically. This means that each one shall feed 
the same number of lamps. This plan is of little value, because 



O O 




Fig, 358.— Feeders With Rheostats. 



the same number of lamps can never be assumed to be burning at 
all times. A general estimate is all that can be made. 

The next cut, Fig. 358, shows an attempted refinement on the 
last described connection. Here each feeder has its own rheostat. 



DISTRIBUTION. 



495 



This makes it possible to vary the resistance so as to maintain 
an even potential drop in the feeder. This method is opposed 
to the general law to the effect that resistance should be con- 
centrated in the lamps, or v^herever heat energy is to be used. 
The putting resistance voluntarily into a feeder or any other 
transmission line is on its face at least bad engineering. The 
voltage should be increased or reduced at the dynamo. Resist- 
ance such as indicated in the diagram is called "dead" resistance. 
Auxiliary Feeder Connections at higher voltage than that of 
the station dynamo are sometimes used. The next diagram. 
Fig. 359, shows this method. To the left is the station dynamo 




jFig. 359.— Auxiliary Bus-Bab. Connection. 



delivering current to the main feeder F'. For auxiliary feeders 
a special bus-bar is provided. This is connected to a special 
dynamo D, which maintains any desired potential in the feeder 
circuit F. A is connected to D by the switch a. 

Transfer Bus=Bar.— Sometimes a feeder supplied from one bus- 
bar of a given potential has to be shifted to another at a higher or 
lower potential. A transfer bus-bar is used for this purpose. 
In the diagram, Fig. 360, A is a high-potential, C is a low- 
potential, and B the transfer bus-bar. Suppose that the low- 
potential feeder M, as the circuit is drawn upon for current in 
the lighting hours of the evening, has to be shifted from C to A. 
The switch c is closed upon B. At cZ is a rheostat. As shown, 
the circuit at d is open. The arm of the rheostat is swung to 
the left, thus closing the contact through the resistance of the 



496 



ELECTRICIANS' HANDY BOOK. 



rheostat. The switch arm d is moved on slowly until an ammeter 
shows that B is taking all its current from A. This can be 
brought about by reducing the resistance by moving the switch d. 




Fig. 360.— Transfer Bus-Bar. 

The switch & is next opened, and d is swung to the end of its 
course, so as to cut out ail resistance. 
Example. — As an example of parallel and feeder distribution 



LINE OF BOULEVARDS 




Bl 



SSSISM27b^ 



^WW<>^^^^^ 



^^^<i?^6^^V^( <^^^^^<:?l'^^ 






^, 



Fig. 361.— Example of PARALLEii Distribution. 



embodying conical leads. Fig. 361 is given, showing a district of 
Paris, which illustrates much which has been described. 

Feeder Economy .—When capital has been invested in tons of 
copper in order to keep resistance down all through a lighting dis- 
trict, it seems crude to regulate the action of feeders by volun- 



DISTRIBUTION. ^^'^ 

tarily increasing their resistance by a rheostat. It seems still 
worse to make them absolutely useless by opening a switch, and 
utilizing an expensive feeder line perhaps only during an hour or 
two of peak. With rheostats some good is got out of the Imes. 
With an open switch the line does nothing. 

It is fair to assume that most stations are operated largely 
for light It therefore follows that for some twenty hours out 
of the twenty-four their mains will be comparatively idle. Hence 
if a main is switched on for only one hour, it is hardly fair to 
say that it is idle for !i of the day. Relatively speaking, it would 
be fairer to refer !ts action to the lighting period, and treat it as 
idle for three-fourths of the time only. 

Three= Wire System .-The three-wire system, like the rest of 
the parallel systems, is a concession in the direction of economy 




Fig. 363.-THBEE-WIBE System With One Generator. 

of copper. The direct source of this economy lies ^^/^^J^^^^Jf ^ 
of the initial voltage of the system. For lamps of 110 volts a 
potential difference of 220 volts between the mams is employed. 
The station dynamo may run at 230 volts. A further economy m 
me exp uses of the leads or conductors is based on the probability 
that'amps can be so distributed into two groups that all he 
lamps in one group will never be lighted at a time when all the 
lamps in the other groups are extinguished. ,, ,^,^^, ... 

m the three-wire system three leads are carried through the 
disTrict, Fig. 362. A potential difference of 220 to 230 volts s 
l:fntained'between two of the wires; the third wire lesjaalf 
way between the others in potential. The third one is caJed 
the neutral wire. One dynamo, as in this cut, or two, as m Fi.. 
363 may maintain the power. , ,, ^ xv, 

saving inCopper.-The saving Is due to the fact that the c^r- 
cult haf its two outer leads maintained at double the potential 



498 ELECTRICIANS' HANDY BOOK. 

difference of that which would be required in the two-wire sys- 
tem. Hence for the same number of watts, and consequently 
for the same number of lamps, one-half the current would be re- 
quired. The two outer conductors could be made one-half the 
size of those in the two-wire system. This would be one-half the 
copper. But the neutral wire has to be provided. This may be 




Three- Wire System With Two Generators. 



smaller than either of the others, but it is always of some con- 
siderable proportion of the size of the main wires. 

If the lamps were always lighted in even number on each side 
of the neutral wire, it could be dispensed with. If all the lamps 
on one side were lighted and all on the other were extinguished, 
the neutral wire would have to be as large as the main wire. Its 






Fig. 364.— Action of the Neutral. Wire. 

relative size is a matter sometimes of calculation and sometimes 
of judgment. 

The diagram. Fig. 364, shows a case typical of the three-wire 
system. The neutral wire here has two currents going through 
different parts of it, in opposite directions. It is like two tides 
coming around an island and impinging against each other. A 
portion of the neutral wire in this case receives no current what- 
ever, yet other parts of it are passing current and keeping the 
system balanced. 



DISTRIBUTION. 



499 



Two=DynamoThree=Wire System.— In first-class station work 
the three-wire system is operated by two dynamos, each of the 
requisite potential to supply a single set of lamps. The cut, Fig. 
365, shows the system. It is clear that each dynamo could sup- 
ply the lamps between its main and the neutral main. The 
neutral wire or main connects with a line connecting the two 
dynamos, one positive and one negative brush, as shown. 



^Tzm 




Ts: 



JB. 



foo 
■o- 






S2 



2Z2: 



^i 6-6- 



oo 
o-o- 



jmw 



^m: 




Fig. 365.— Three-Wire System With Two Dynamos. 



Single=Dynamo Three=Wire System.-Various modifications of 
the three-wire system are employed in special cases. One is 
shown in Fig. 362, in which the neutral wire does not connect 
with the single dynamo used. This dynamo must have twice the 
voltage required for a single lamp in addition to that required 
for the drop. 

Three=Brush Dynamo. — Another modification consists in the 
introduction of a third brush on the dynamo, placed midway be- 
tween the regular ones. The neutral wire is connected to this 
brush as shown in the cut, Fig. 366. The system is apt to give 
a great deal of sparking on the commutator if the two circuits 
take different currents. The normally idle neutral wire at least 
supplies a security against the obligatory shutting off of two 



500 



ELECTRICIANS' HANDY BOOK. 



lamps at once. Where there is little chance of great inequality 
between the two groups, such an arrangement will work very- 
well. It is not to be regarded as 
a standard method, on account of 
the liability to sparking on the 
commutator. 

Storage Batteries in the 
Three=Wire System can be used to 
advantage. The cuts. Figs. 367 
and 368, show three-wire systems 
with storage batteries. When 
lamps are extinguished, the sur- 
plus current from the dynamo 
goes through the battery and 
charges it. When the current 
from the dynamo is drawn upon 
beyond its fullest extent, the stor- 
age battery comes into action, and 




-o- 



o- 



o- 




rn 



T 



X 



Pig. 366.— Three-Brush 
Dynamo. 



Figs. 367 and 368.— Storage Batteries in 
Three- Wire System. 



supplies the deficiency. Its action is regulated by the use of end 
cells, counter electromotive force cells, or rheostat, as elsewhere 
spoken of. 



DISTRIBUTION. 



501 



Storage Battery Equalizer in Three=Wire System,. — In Fig. 
369 the storage battery S is connected to the neutral wire N and 
to the outer wire M. If lamps are extinguished on one side of 
the system, the current thus thrown upon N is taken care of 




Fig. 369.— Three-Wire 'System With Storage Battery Equalizer, 

by the battery. It will charge or discharge according to which 
group A or B is using most watts. A rheostat is provided to regu- 
late the dynamo field. The battery could be connected to P in- 




FiG. 370.— Balancing Dynamo in Three-Wire System. 



stead of to M, but not to both without abandoning this particular 
arrangement. 
Balancing Dynamo. — The illustration, Fig. 370, shows two 



502 



ELECTRICIANS' HANDY BOOK. 



dynamos in a three-wire system, one, indicated by A, being of 
double the voltage of B. Both are driven from the same counter- 
shaft E. At even load on both branches, P and M, the dynamo B 
runs idle. If the branch P has most load, current going through 
the neutral wire goes through B and actuates it as a motor. If 
M has most load, B operates as a dynamo to supply the M side 
of the system. 

Motor and Booster.— In the cut. Fig. 371, A represents a dyna- 
mo running at a high enough potential to make the loss between 
G and R comparatively small. A is in the central station, R and 
C are in the district. R is a motor, and its functions are to drive 
the booster C. 




Fig. 371.— Motor and Booster in Three- Wire System. 



Five and Seven=Wire System. — The three-wire system is the 
first step in multiple wiring, as a two-wire system does not fall 
into the category of multiple wiring, where it etymologically 
should belong. The next step is to add couples of wire. Thus 
the five-wire and the seven-wire system are developed. In the five- 
wire system the potential is four times that of a single lamp; 
in the seven-wire system it is six times that quantity. If stand- 
ard incandescent lamps are used, the voltage of the systems will 
be 120 X 4 =: 480 volts, and 120 X 6 = 720 volts, allowing for the 
drop of the lines. 

The central wire is the neutral wire, but the current may be 
variously divided among the wires by the consumption varying 
in different groups. 

The high voltages are not very safe, and it can be readily seen 



DISTRIBUTION. 503 

that such a multiplication of wires complicates the station ma- 
chinery and the distribution of lamps on the circuits. The at- 
tendant high voltage exacts better insulation and more careful 
laying of mains and leads. In America the three-wire system 
has obtained by far the greatest extension. In Europe the five- 
wire system is used in a number of places. 

Examples of five-wire systems are shown in Figs. 372, 373, and 
374. The last two illus- 
trate the use of storage ^ ^^ 

batteries at the station J j i O 



end of the system. They f^\ 9 o O" 

are susceptible of many ( j i ^ ^" 

variations. ^^_V^ ^ — ^ 



High - Voltage ParaN f 9 9 
lei Systems. — The manu- 
facture of 220-volt lamps . _j_ _ __■ 

has been considered a dif- J^ -r y y Q, 

ficult problem to solve /^^ ^ -^ A A Q 

under commercial limits. ( J Jti 1 l ^ 

With such, a three-wire V,.-^/ "T " . T ^ 

system could be operated [ -j- y j ^21. 

at 480 volts minimum, re- 
ducing the copper used 



for mains to one-half the r\ "T 1 1 



>? ^ 6 



amount for 110-volt V^ -^^^ E 5 ^ 

lamps. Some authorities /Z~ ~T~ J~"i~^ o" 

consider that the three- ( | "p 1— p- J — j^ ^- 

wire system with 220-volt ^^ y^ -r ? r Q_ 



lamps is destined to pre- j-iQg, 373^ 373 j^^j^ 374.-Five.Wire Systems. 
vent the extensive use of 

the five-wire system. Multiple-wire systems possess a fea- 
ture which may be of value. There is nothing in the system 
to interfere with the possibility of connecting apparatus such 
as motors across from main wire to main wire, thus utiliz- 
ing the double voltage of the system with the exclusion of 
the neutral wire. A 220-volt motor can thus be used on a 
three-wire 110-volt circuit. On a five-wire or seven-wire sys- 
tem the entire potential difference will approximate respective- 



504 



ELECTRICIANS' HANDY BOOK. 



ly 480 and 720 volts. This gives the conditions for a high- 
power motor with small conductors. The voltage in such cases 
is about that of a trolley car system, and the system repre- 
sents a combination of high and low voltage parallel distribu- 
tions. 



TRANSFORMERS ARRANGED IN SERIES, 
WITH LAMPS IN PARALLEL. 




TRANSFORMERS ARRANGED IN SERIES, 
WITH LAMPS IN SERIES. 




TRANSFORMERS ARRANGED IN PARALLEL, 
WITH LAMPS IN PARALLEL.. 

Figs. 375, 376 and 3T7.— Examples of Transformer Distribution. 



Alternating=Current Drstribution.— The use of the transform- 
er to change voltage is the characteristic feature of this class of 
distribution. Fig. 375 shows in diagram transformers in series, 
each absorbing a portion of the voltage of a dynamo and trans- 
forming it into voltage adapted for lamps, which are supplied in 
parallel from the secondaries. Fig. 376 shows a series of trans- 
formers as before, but each one supplying a set of lamps in series. 
A full parallel system is shown in Fig. 377, where the transformers 



DISTRIBUTION. 



505 



are in parallel, their primaries connecting to two leads from a 
dynamo, and lamps in parallel being supplied from each trans- 
former. The lamps as in both the preceding cases take current 
from the secondaries. The latter arrangement is shown more in 
detail in Fig. 378, where arc lamps absorbing 104 volts each are 
supplied by means of a converter from a 1040 or 2080 volt circuit. 




Fig. 378.— Transformer Connection for Arc Lamps. 



Individual Transformers. — Small transformers are used for 
single motors and lamps. In Fig. 379 is shown a motor supplied 
from a high-tension circuit by means of a transformer. This 
and the preceding cut have the names of the different parts noted 
on th-e illustration. Although only one motor is shown, the ex- 
tension of the secondary circuit to right and left indicates that 
more motors may be supplied by the same transformer. 

Clioke Coils. — In Fig. 380 is shown a single incandescent lamp 
carried on a bracket with a receptacle at its base in which there 



506 



ELECTRICIANS' HANDY BOOK. 



is a choke coil. This is virtually a transformer without any sec- 

ondary. It is connected in 

parallel with the lamp. An 
alternating current as often 
thus connected lights the 
lamp because the inductance 
of the coil sends current 
through the lamp. If the 
lamp filament breaks, the cur- 
rent goes through the coil. 
Thus the breaking of the lamp 
does not break the circuit. 
The arrangement is adapted 
for lamps in series, as shown 
in Fig. 381. 

Y Connection for Alter- 
nating Current. -Three-phase 
alternating current is often 
distributed by the Y connec- 
tion, so called because the 
three leads are connected as if by a letter Y, The diagram. 




Fig. 379.— Motor and Individual 
Tkansformer. 




'.—Choke Coiii for Incandescent Lamp. 



Fig. 381a, shows the system. At the generator end the arma- 
ture windings A, B and C are connected at a central point n. 



DISTRIBUTION. 



507 



This is described elsewhere under the subject of alternating cur- 
rent generators. From the ends of the three windings three 
leads are carried through the district and la^mps or motors are 
connected as indicated, A motor is indicated on the right hand 
.with its three armature coils, A, B and C, also connected at a sin- 




lOlOO VOLT LAMPS IN SERIES. 



Fig. 381.— Incandescent Lamps in Series With Choke Coils. 



gle point n. The lamps are connected between any two leads as 
shown. If there are more lamps on one pair than on another 
the system will be out of balance, and a fourth neutral wire con- 
necting n and n will be required. This is sometimes called star 
connection. 
Delta Connection. — This is also spoken of under alternating 



508 



ELECTRICIANS' HANDY BOOK. 



current generators and is illustrated in Fig. 3816. A, B and C 
represent the three armature coils of a three-phase generator and 




GENERATOR 







LINE 






tl A 






B^ 


•^H 


LINE 




^ 










LINE 


< 



-i — ^-^ 




UMj»a 



^ 




GENERATOR MOTOR 

Figs, 381a & 3817).— Y and Delta Connections fob Alternating Currents. 



F=ffiMII]?S^ 




Figs. 382 and 383.— Iron Wire Joint and Tib. 



motor respectively connected as shown. No neutral wire is used 
in this system. 

Joints in Line Wire.— It is beyond the scope of this work to 
give the details of line construction, which is becoming more 



DISTRIBUTION. 



509 



complicated as aerial and underground distribution systems ac- 
quire more extension. In the illustrations, Figs. 382 to 390, some 
examples of joints and ties in wire conductors are given. 

Figs. 382 to 386 show how iron wires are joined to each other 
and how they are tied to glass insulators. The joint shown in 
Fig. 382 is sometimes called the Western Union joint. The tie 
wire in Fig. 383, it will be observed, is carried around the insu- 
lator, and its 6UdS SHQ then twisted around the line wire. Other 




Figs. 384 and 385.— Iron Wire Tees. 



Fig. 386.— Putting on Ties. 



ways of tying are shown in Figs. 384 and 385. In one the tie 
wire does not go entirely around the insulator, in the other it 
completely encircles it and is twisted once around itself before 
the ends are twisted around the line wire. Fig. 386 shows th-e 
operation of making such joints. 

For copper wire, sleeve joints have met extensive use. The 
Helvin joint was made with a brass double sleeve receiving the 
ends of the wire. One way of using a sleeve is to twist the ends 



510 



£J LE C TRIG IAN S' HANDY BOOK, 



of the wires projecting beyond the sleeve around the line wire 
outside of the sleeve. The ends of the sleeve are closed with 
solder. 

Fig. 387 shows such a double sleeve used in the Mclntyre joint. 
Here the wire is passed well into the sleeve, and then wire and 
sleeve are twisted together as shown. Sometimes solder is ap- 




FiGS. 387 AND 388.— Slejeve Joint's. 

plied, holes being made in the sides of the sleeve to admit the 
solder. 

A simple strip of copper bent so that its cross section is S-shaped 
is used as in the Mclntyre tubular sleeve. It is shown in Fig. 388. 
A simple joint made with a small wire seizing is shown in Fig. 
389. Soldering may be applied to this joint. 

Ends of wires in cables are joined by twisting, as shown in 



Fig. 389.— Seized Joint. 

Fig. 390, care being taken to prevent the wire at the joint in one 
wire from touching that in another. When ends of cables are to 
be connected, a lead sleeve is placed over the end of one cable, is 
pushed back, and the wires are connected and the joints are insu- 
lated by paper wrapping or other material. The sleeve is then 



DISTRIBUTION. 



511 



pulled over the joint and soldered to the ends of both cables in- 
closing the joint, so as to make it perfectly water-tight. Such a 
sleeve soldered in place is shown in Fig. 391. 

In Fig. 392 is shown the transposition of wires on a pole top. 
This is done in order to avoid induction; the induction inevitable 
when an active telegraph or telephone wire is near another one. 





Fig. 390.— Joining Wires in a Cable. 



Fig. 391,— Sleeve on Cable. 




Fig. 393.— Transposition in Aerial Line Work. 



being of opposite polarity as the leads are changed. Thus the in- 
ductive effect from one length of wire counteracts that from the 
other. 

Insulators. — These are now made in a great variety of forms. 
As typical of modern practice two insulators are given in the 
cuts. Fig. 392a is an insulator with a groove in its top to carry 
the wire, and constructed to withstand a potential difference of 
80,000 volts. By doubling the projecting flanges or "petticoats," 



512 



ELECTRICIAIS'S' HANDY BOOK. 



the insulator shown in Fig. 39 2& is made, which is good for a po- 
tential difference of 120,000 volts. These are extreme cases. 




Figs. 392a and 392&.— High-Tenston Insulators. 

In former practice there were comparatively few forms of in- 
sulators, but the recent development in the use of high-tension 
circuits has brought a great many forms into the field. The 
problem of adequately insulating a line with a potential difference 
of thousands of volts backed up by a heavy current is widely dif- 
ferent from insulating a telegraph line. 



CHAPTER XXIX. 

ELECTRIC METERS. 

Electric Meters may measure current irrespective of voltage 
when they are current meters. They may measure the current 
and voltage w^hen they are wattmeters. 

Wattmeters operate correctly where electric power is sup- 
plied, but not for incandescent light unless a constant voltage 
is maintained. They only correct for about /Dne-flfth of the de- 
ficiency in light suffered by the customer or excess obtained by 
him on changes in voltage. An over-compounded wattmeter 
would seem to be the best for light-supply metering, one which 
for a change of one volt would change the reading about six per 
cent. 

Edison's Meter, — This meter was conceived on the somewhat 
heroic principle of the collection and weighing of metal deposited 
in meters by electrolytic action. The meters gave no direct read- 
ing. To get at their results, small quantities of zinc had to be 
weighed for each meter periodically, and the current supplied was 
taken as being proportional to the weight of this zinc. For years 
the meters in cities supplied by the Edison system were thus taken 
by the operative in charge. Baskets filled with electrodes were 
transported to the station, and the electrodes were individually 
weighed, and the current supplied was calculated on this electro- 
chemical basis. 

The cut. Fig. 393, shows its construction. It contained two 
cells, each containing a pair of amalgamated zinc electrodes. 
They were made of as pure zinc as possible, and before amalgama- 
tion were coated with zinc by electro-deposition. The cells con- 
tained a solution of zinc sulphate of 1.11 specific gravity. The 
meter had in series with the plates a coil of copper wire. The 
resistance of copper wire increases as the temperature rises, just 

513 



514 



ELECTRICIANS' HANDY BOOK. 



as does that of other metals. This was to compensate for the 
fall of resistance with rise of temperature which occurs in the 
solution. The meter was placed in shunt with a known resistance 
on the line, and its own resistance being known, it received a 
fraction of the total current equal to the quotient of its own resist- 
ance of the portion of the line in parallel with it divided by the 

resistance. The weight 
of zinc deposited gave 
the coulombs of electric- 
ity used. An incandes- 
cent lamp was automatfc- 
ally lighted by an expan- 
sion bar when the tem- 
perature fell, and extin- 
guished as it rose. 

The same principle 
was applied to a register- 
ing meter. The plates 
were hung at opposite 
ends of a scale beam, 
and were alternately 
subjected to one or the 
other action, so as to 
move the beam from 
time to time. Each 
movement was due to a 
deiinfte deposition on one 
plate and dissolving of 
the other. As the beam 
swung it reversed the 
current, and after a cer- 
tain amount of coulombs had passed, it swung back. The swings 
were registered by clockwork or geared mechanism of the regular 
type. 

A counter electromotive force of 0.001 to 0.003 volt caused the 
readings at low current to be erroneous. 

Forbes Heter This meter was actuated by the heat produced 

by a current. In the lower part of a glass shade there was a flat 





Fig. 393.— Edison's Chemical Meter- 
Section al Diagram. 



ELECTRIC METERS. 



515 



coil of wire which occupied a horizontal position. Above it was 
a vane with four inclined wings like a little screw propeller. This 
vane worked in very delicate bearings. The current to be meas- 
ured or a known fraction of it passed through the coil and heated 
it. The heat caused an air current to rise from the wire, and this 
turned the vane windmill fashion. The turns of the vane were 
registered by machinery. 




Fig. 394.— Thomson's Induction Meter. 



Thomson's Meter.— This meter, due to Elihu Thomson, is a 
wattmeter and is shown in part section in Fig. 394. It consists 
of two field coils without iron core, through which the entire 
current which is to be measured passes. Within the coils an arm- 
ature coil without iron core is mounted. It has a commutator. 
It receives current from the wires of the circuit, being connected 
across them with high resistance interposed. It receives current 
proportional to the voltage existing between its places of attach- 
ment. The field coils of low resistance receive all the current prac- 
tically that passes. The armature rotates and drives an indicating 



516 ELECTRICIANS' HANDY BOOK. 

train of wheels like that on a gas meter. A horizontal copper 
disk rotates on the vertical axis which carries the armature, and 
steel magnets with poles brought near together embrace the outer 
portion of the disk between their poles, and constitute a brake on 
the rotation of the armature. The speed of rotation is due to the 
field acting on the armature. The strength of the field is due to 
the amperes of the current; the strength of the armature is due 
to the voltage of the circuit; the reading of the meter is due to the 
combined effect or to the volt-amperes or watts. 

The meter is primarily a shunt-wound motor. An auxiliary 
field coil in series with the armature gives it the character to a 
limited extent of a compound-wound meter. This field with the 
armature develops alone almost enough torque to turn the arma- 
ture. It therefore takes care of the friction of the meter in great 
part, so that the magnetic brake opposes all the resistance to its 
motion, a resistance increasing v/ith the speed. 

It will be seen in the cut. Fig. 394, that the permanent magnets 
are held in position by screws going through a horizontal bar, 
a portion of the frame of the meter. These can be loosened if 
desired, and the magnets can thus be moved in and out. This 
operates to regulate the meter and make it move faster or slower. 
It can thus be tested with lamps, and adjusted over a range of 
about 16 per cent. An alternating or direct current can be meas- 
ured by this meter. 

For three-wire systems, one of the field coils takes the current of 
one active wire; the other coil that of the other active wire. The 
coil in circuit with the armature is connected across from the 
neutral wire to one of the outer wires, thus getting the voltage 
of one lamp, or customer's voltage. Sometimes the shunt field 
coil and armature are connected across the outer wires, thus 
taking twice the voltage. A transformer can be used in alternat- 
ing current supply where the voltage is too high for the resist- 
ance of the meter. In meters for heavy currents a single copper 
bar passing between two armature coils constitutes the field. 

For two and three-phase alternating-current circuits a combina- 
tion of two or three meters in one is made. One dial gives the 
reading. Otherwise, two meters can be connected to give the 
readings of three-phase systems. The sum of their readings is 



ELECTRIC METERS. 517 

taken. If the lag exceeds 60°, giving a power factor of less than 
one-half (cos 60° = %) one of the wattmeters will have a negative 
reading, in which case it must be subtracted from the reading 
of the other one. 

For series systems the field is in series with one of the main 
conductors, so that the full current, which is not a very high one, 
goes through it. The meter gives watt hours. 

Shallenberger's fleter.— The entire current passes through a 
fixed coil of few turns. Within this coil is a second one with 
self-contained re-entrant circuit, constituting an induction motor 
armature, as it has no outside connection. Its axis is at an angle 
with that of the outer coil. When an alternating current passes 
through the outer coil, it induces a current in the closed circuit 
of the inner coil. A reaction is established with a resultant field 
between the two fields, one of the outei: and the other of the 
inner coil, which fields are not coincident in position, but lie at 
an angle to each other, equal to the angle between the axes of the 
coils. There is also a difference of phase between the two coils, 
which causes the resultant of the fields to rotate, thus constituting 
a rotary field. A vertical arbor or spindle carries a horizontal 
metallic disk which lies in the field, and is acted on by the 
rotary field when current passes, and caused to rotate. To retard 
its motion, air vanes are carried by the spindle. The principle 
of the meter is that the torque increases with the square of the 
current, being due to the energy expended. The resistance offered 
by the vanes varies with the square of the speed. Thus, the 
speed of rotation of the disk is directly proportional to the cur- 
rent strength. This meter is a current measurer, taking no di- 
rect cognizance of the volts of the circuit. 



f 



CHAPTER XXX. 

LIGHTNING ARRESTERS. 



Lightning Protectors. — Atmospheric electricity produces dis- 
turbances in electric apparatus unless means are taken to give it 
a way of escaping to the ground. Whatever the nature of the 
disturbance, so great a voltage is established that the current 

due to the atmospheric electric- 
ity can jump across an air gap 
quite impassable for working 
electrical currents. 

Comb or Saw=Tootli Arrest= 
er.— This was one of the early 
protectors. Attached to the 
line to be protected was a plate 
with a series of saw teeth on 
one edge. The plate might be 
an inch long. A similar plate 
faced it tooth to tooth, both 
being screwed flat on a board. 
The second plate was connected 
by a conductor to the earth. 
Ordinarily the working elec- 
trical apparatus would contain 
electro-magnets or similar ap- 
pliance of high inductance. If 
a disturbance occurred, produc- 
ing a discharge on the line, the regular apparatus by its induc- 
tance would choke back the discharge, which would jump across 
the gap from one set of teeth to the other, and so escape to the 
earth. 

riagnetic Blow=Out Arrester. — This is shown in Fig. 395. The 

518 




Fig. 395.— Magnetic Blow-Out 
Lightning Arrester. 



LIGHTNING ARRESTERS. 



519 



two flaring plates of metal approach each other closely at the 
lower end. One is connected to the earth, the other to the line. 
An electro-magnet is in the line circuit. Lightning on the line is 
choked back by the magnet, owing to its inductance springs 
across the gap, and goes to the earth. Any arc which it may 
form is blown out by the magnet. It is driven toward the diverg- 
ing ends of the plates, and breaks. The three connections to 
line, earth and machine are indicated in the cut. 

Non-Arcing Metal Arrester. — This arrester is made up of a 
number of cylinders of 
metal of the cadmium 
group or near it, which 
does not readily main- 
tain an arc if in the po- 
sition of electrodes. Fig. 
396 shows the construc- 
tion. The seven cylinders 
have about one-thirty- 
second inch of air be- 
tween each two. The ex- 
terior or end cylinders 
are connected with the 
line, and the central cyl- 
inder is grounded. The 
other four serve to form 
the additional gaps. With 
alternating currents this 
arrester forms no arc 
after a discharge; with 
direct current it may form a harmless one. 

Discriminating Arresters. — This name is due to Mr. A. J. 
Wurtz, the inventor of the last described as well as of this ar- 
rester. Two brass terminals an inch wide are laid in grooves and 
flush with the surface of a block of marble. Their ends come 
within half an inch of each other. A piece of lignum vitae fllls 
the gap between their ends and across it are made a series of 
charred grooves about one-tenth of an inch wide and one-thirty- 
second of an inch deep. A cover of marble is secured over it. 




Fig. 



-Non- Arcing Metal Lightning 
Arrester, 



520 



ELECTRICIANS' HANDY BOOK. 



One plate is grounded; the other is connected to the line. No 
ordinary current can pass over the charred surface, which acts to 




'l|TO|jT]T[l|i!iiiiiiinniiiiiiiiiniiJjyijJ 


Fl" ''""J 


lBiiiiiiiiiiiiiiiiiiiiiiii|iia! 



Figs. 397 and 398.— Wurtz's Carbon Lightning Arrester. 

LINE 





Fig. 399.— Westinghouse Lightning 
Arrester. 



Fig. 400.— AliTERNATING 

Current Lightning 
Arrester. 



LIGHTNING ARRESTERS. 



521 



conduct the atmospheric discharge to the earth. No arc forms 
in this apparatus. The resistance of the apparatus may be as 
high as 50,000 ohms. Sometimes no marble is used, the electrodes 
being screwed directly to the wooden block of lignum vitge. It is 
shown in Figs. 397 and 398. 

Westinghouse Lightning Arrester.— A disk-shaped choke coil 
is carried on an insulator, as shown in Fig. 399. This coil has 
sufficient inductance to oppose the passage of a lightning dis- 
charge, yet not enough to seriously affect the current. To the 





Line Line 'Line Line 

Flgs. 400a. AND 4005.— Double-Pole Light- 
ning Arresters. 



right are non-arcing spark gaps. The line is connected above 
and below the coil; the lateral connection gives the path for 
the lightning discharge, which goes to the earth through the ar- 
resters, which are of one of the types already described. 

Low- Equivalent Alter nating= Current Lightning Arrester.— 
In Fig. 400 is given a diagram of an alternatfng-current lightning 
arrester for high-voltage currents. Its action is as follows: The 
discharge springs across the gaps and goes to the earth. Any arc 
formed in the shunted gaps is destroyed by the path for the cur- 
rent offered by the shunt resistance. The series resistance is 
made as non-inductive as possible, and acts to reduce any current 
which follows the discharge. A certain amount of the discharge 
goes through the shunt resistance. 



522 



ELECTRICIANS' HANDY BOOK. 



Double-Pole Lightning Arrester. — The diagrams, Figs. 400 a 
and b, illustrate double-pole connection of lightning arresters, where 
they are connected like lamps across the two leads of a circuit. 

Tank Lightning Arrester. — This arrester is found particularly- 
serviceable on electric railways. Choke coils carried on a slate 
or marble base are put in the circuit, as shown in the upper part 




Fig. 401.— Tank Lightning Arrestek. 



of Fig. 401. Conductors from the coils run down to a tank of 
water shown in the lower part of the cut. Water is run through 
the tank when a storm threatens. A slight current leakage 
constantly takes place, but is trifling. If a lightning discharge 
occurs, it goes to the earth by way of the tank. The choke coils 
force it to the tank. 



CHAPTER XXXI. 

THE INCANDESCENT LAMP. 

Incandescent Lighting. — The incandescent lamp is the expres- 
sion of a fundamental law of electric supply, which is to the 
effect that resistance in an electric circuit should be concentrated 
at the point where energy is to be developed. If a circuit is de- 
voted to running machinery, the resistance should be in the ma- 
chines, and as little resistance as possible should be in the lines. 
If lamps are to be lighted, as much of the total resistance as pos- 
sible should be concentrated in them. 

In the case of incandescent lighting, the useful resistance is 
that which is produced by the filaments of the lamps. All re- 
sistance not manifesting itself through heating the thin fila- 
ments represents lost power and waste of energy. It is a curious 
thing that the useful energy of every horse-power in an incan- 
descent electric-light system is represented by the ignition of 
only five or six feet of carbon filament. 

The Incandescent Lamp comprises a filament of carbon of 
various shapes, approximating to a letter U. The filament is 
inclosed in a glass bulb within which a vacuum is produced. 
"Wires passing through the glass are connected to the source of 
current, which heats the filament bright red or white hot, so that 
it emits light. 

Tamidine Filaments. — Weston made for the basis of filaments 
a substance which was named tamidine. It was prepared from 
solid massive nitro-cellulose, the substance left by the evapora- 
tion of collodion, so familiar to the old-time photographer, and 
now used for surgical treatment of minor cuts and the like. 
The nitro-cellulose was reduced by a chemical reducing agent 
such as sulphureted hydrogen, converting the mass completely 
or nearly into cellulose. This material resembled transparent 

533 



524 ELECTRICIANS' HANDY BOOK. 

horn. Filaments were cut out of it, were carbonized, and used 
in lamps. 

Squirted Filaments. — Filaments are now made also by forcing 
the proper material through a die. A thick solution of nitro- 
cellulose, which is a syrupy collodion, can be forced through a 
fine aperture and evaporated, giving a thread. This after reduc- 
tion could be used as a basis for filaments. Cotton can be dis- 
solved in a solution of zinc chloride, giving a syrupy transparent 
solution. This can be forced through an aperture into a vessel of 
alcohol. This hardens the thread so that it can be handled. The 
zinc chloride is washed out of it as far as practicable, and it is 
eventually wound on drums as a long thread, resembling the 
fisherman's silkworm "gut," which is attached to the fishhook. 

The thread made as described is cut into the proper lengths 
ready for carbonization. Various practical details have to be 
followed. Bubbles are one of the troubles. The thick solution 
retains these with some persistence, and heating the solution in a 
vacuum is sometimes used to expel them from the solution. Per- 
fect evenness of the solution is secured by thorough stirring, and 
an exact formula for the solution is followed. The purified cot- 
ton prepared for physician's use under the name of absorbent 
cotton is the best material for the process. Filaments made by 
this method are called "squirted filaments." 

Carbonization is effected by heating the thread to redness in i 
an oven. It is protected from the air by being imbedded in 
powdered charcoal, or by some method by which no oxygen can 
reach it while heated. It would instantly burn if air had access 
to it while at a red heat. 

Calibration. — As the process is usually carried out, the thread 
from the circular die is still somewhat soft when wound off upon 
the drum, and the winding flattens it a little. It is necessary to 
have filaments of exact dimensions, so the filament of oval section 
is calibrated in two directions to determine its cross-sectional 
area after carbonization. Filaments are thus sorted out for 
various resistances. The length is not so conveniently changed, 
as the bulb is supposed to be suited for a certain sized loop of fila- 
ment. 

Flashing.— The filaments from the carbonizing oven are next 



THE INCANDESCENT LAMP. 525 

flashed. This process was a very -early conception. The electric- 
light filament is increased in density, elasticity, and hardness by it, 
its pores being filled and its surface being coated with graphitic 
carbon. A number of the filaments are fastened by holders of 
metal to the stopper of a jar. This jar is filled with vapor of 
naphtha or other hydrocarbon, and the stopper is inserted with 
the filaments on its inner side protruding into the jar. A current 
is passed through them, igniting them to bright redness. The 
thin parts get hotter than the thick ones. The hydrocarbon is 
decomposed when it com-es in contact with the hot filament, and 
more of it is deposited where the filament is hottest, which is 
where it is thinnest. Thus fiashing not only solidifies the fila- 
ment, but builds up its thin places. 

Occlusion of Gases by Filament. — A porous solid has some- 
times a peculiar action on gases which is termed occlusion. Gases 
will thus be retained much as water is retained by a sponge. The 
thread of cellulose or cotton before carbonization is as absolutely 
without pores as anything can well be, but in the carbonization 
process it becom-es full of pores, and these may occlude oxygen. 
When such a filament is placed in an exhausted bulb, all of the 
gases may not be given up until ignition is applied by the cur- 
rent. If gas is thus introduced into the bulb, it will have a bad 
effect upon the filaments. The flashing process fills the pores, 
and gets rid of occluded oxygen by combustion as well as ignition. 

Lowering, of Resistance by Flashing.— The flashing process 
lowers resistance 10 to 15 per cent, so due cognizance must be 
taken of this action in sele'^ting the size of fllament for any given 
lamp. It is easy to bring about any desired resistance by flash- 
ing, and the resistance can be determined if desired from time to 
time during the process. The logical way of determining resist- 
ance is to do it while hot, as the resistance of a lamp when cold 
is only an indirect factor as far as its use is concerned. 

Making Joints by Flashing.— The filament has to be fastened 
to a wire at each of its ends, and an interesting application of 
flashing is the making of a joint between these wires and the 
filament. It is made by flashing the fllament in a hydrocarbon 
vapor or even in liquid naphtha through the wires held against 
the ends of the fllament. A solid coating of hard graphite is 



526 ELECTRICIANS' HANDY BOOK. 

thus formed around wire and filament end, just as if a soldered 
joint were made. 

Pasted Joints.— An easier and cheaper way to make the joint is 
to put a little putty-like mixture of finely-powdered carbon and 
molasses around the junction of filament and wires. On ignition 
this hardens and forms a secure joint. 

Electroplated and Other Joints.— These are made by electro- 
lytic soldering. A coating of copper is deposited over the junc- 
tions of wires and filaments by electroplating, forming a conduct- 
ing coating over wire and filament ends. The joint has often been 
made by a very small bolt, which passes through holes in the 
enlarged ends of the filament and wire, and has a nut screwed on 
its end. Another system is to have sockets in the ends of the 
wires, into which the filament ends are thrust. The flash joint 
and carbon paste joint are the principal ones used in recent prac- 
tice. 

Leading=in Wires.— The solution of the problem of passing a 
wire through glass and then melting the glass around it so as to 
form. an air-tight joint hinges on the coeflacients of expansion by 
heat of the metal and glass. These must be practically the same, 
or else the wire will work loose from the glass, forming cracks, 
perhaps very minute yet sufficient to admit air. All sorts of com- 
binations of different kinds of glass and metals have been tried. 
The practice has now settled down into the use of platinum lead- 
ing-in wires, which are passed through holes in the glass. The 
glass is then melted around the wires. The metal platinum ex- 
pands and contracts under changes of temperature almost exactly 
as much as glass. It possesses another property of considerable 
importance, which is that it is inalterable under any ordinary 
range of temperature. It will not oxidize at any temperature, and 
melts only at very high heats, far higher than any to which it is 
exposed in the construction or operation of the incandescent lamp. 
This use of platinum has drawn very largely upon the supply, 
and its tendency is to rise in price. The lamp maker uses as 
little as possible, electrically welding copper wire to the platinum, 
so as only to use enough of the rarer metal to pass through the 
glass. 
flaking the Lamps.— The methods differing in details, the fol- 



THE INCANDESCENT LAMP. 



527 



lowing cut. Fig. 402, gives a typical process. No. 1 shows a glass 
tube closed at the upper end, with the leading-in wires passing 
through it, melted in, and with the carbon filament attached. 
No. 2 shows the globe with long exhaust tube with the filament 
thrust into it. No. 3 shows the melting together of the two pieces 
of glass with a blow-pipe flame. No. 4 shows the lamp with 
filament tube melted in ready for exhaustion, and No. 5 shows 
the lamp after exhaustion with its exhaust tube melted off, the 
lamp being ready for use. 

Vacuum.— The bulb of an incandescent lamp after the carbon 




Fig. 403.— Making Incandescent Lamps. 



is in place is exhausted until a very high vacuum is produced in 
it. The vacuum was originally designed to prevent the carbon 
from burning, but it accomplishes other results also. It keeps 
the filament hotter. If the bulb is filled with an inert gas, the 
gas under the effect of the hot filament enters into active circula- 
tion, cools itself against the sides of the bulb, gets heated by the 
hot filament, and then is cooled again. The filament has to heat 
the gas over and over again, and the temperature is materially 
lowered by the process. The efficiency is thus diminished. 

An exhausted bulb is much cooler when the filament is giving 
light than if it were filled with inert gas. As a mere matter of 



528 ELECTRICIANS' HANDY BOOK. 

convenience this is desirable. It is a good feature about the in- 
candescent lamp that its bulb cannot burn the hand, or set fire to 
anything und-er normal conditions, although it is not altogether 
safe to leave burning lamps wrapped up in a combustible wrap- 
ping for a considerable period. 

Production of Vacuum. — The Torricellian vacuum, Fig. 403, 
such as exists above the mercury in a barometer tube, is one of 
the best vacuums produced without special care or for special 
ends. The Sprengel and the Geissler pumps are based upon the 
production of this vacuum. In these air pumps the piston is 
represented by a column of mercury, and the force driving the 
piston is represented by the pressure of a column of mercury over 
30 inches high. A quantity of the lamps are sometimes exhausted 
to a pretty high vacuum by a mechanical air pump, and the ex- 
haustion is finished by the use of a mercurial pump. This re- 
moves the last air, whose removal is facilitated by passing a 
current of electricity through the filament, heating it as the close 
of tlie operation is reached. This expels any occluded and other 
gas held by the wires, glass or filament. Sometimes a little 
phosphorus is put into the exhausting tube and is heated from 
the outside by applying a fiame or other source of heat to the 
glass on which the phosphorus is lying. It combines with any 
trace of oxygen present. To prevent danger to the health of the 
operatives, and to avoid liability of ignition of the phosphorus, 
the modification called red phosphorus is best for this purpose. 

External heat can be applied to the lamp during the last of 
the exhaustion to assist the operation. The exhaustion is done 
through a tube extending from the top of the bulb. This tube is 
melted off in the blowpipe flame when the exhaustion is com- 
plete. The point seen on the end of the bulb shows where the 
sealing was effected. 

The flercury Air Pump.— The Sprengel pump utilizing the 
Torricellian vacuum is shown in Fig. 404. At the top of the 
pump is a horizontal pipe, through which mercury is passed. 
At D D are cocks admitting it to the pumps, one of which is 
shown on the left. The mercury descends through B, goes M 
through the inclined tube down T and out through D' D', to be J| 
repumped into the upper pipe. R is a glass vessel containing a 



THE INCANDESCENT LAMP, 



529 



drying agent, such as phosphoric oxide or sulphuric acid. At O 
is an opening into which the exhausting tube a on the upper 
end of the lamp L can be sealed. It has another opening at S 
communicating with T. The mercury as it leaves the inclined 
tube, if there is a trace of air in R, breaks up into little columns 





Fia. 403.-TORRICELLIAN VACUUM. FiQ. 404.-Sprengel's Air Pump. 



and draws the air down and out. The filament is heated during 
the process by a current adjusted in intensity by the resistance 
coils F F. 

In modern works various kinds of special pumps are employed 
to work on the large scale, exhausting a number of lamps simul- 
taneously. 



530 ELEGTRICIANS'- BAJSfDY BOOK.:' 

The Geissler air pump is operated by the agency of a column of 
mercury, but involves the raising and lowering of a reservoir of 
mercury. The Sprengel pump is described as a typical mercurial 
air pump. 

Luminescence is the quality of giving light when heated. All 
substances possess more or less of this quality, some in higher 
degree than others. Luminescence of a very high degree is shown 
by the Welsbach incandescent gas light. A filament of its ma- 
terial would represent an almost ideal substance for an incan- 
descent lamp filament if it was heated so as to become a con- 
ductor. 

Metallic Filaments have been tried for incandescent electric 
lamps with very little success. Their fusibility is the principal 
objection to their use. At present the metals osmium and one or 
two others are being tried. 

Oxide Filament. — There are substances which are free from 
most of the objections which attach to carbon and the metals, 
except that they normally do not conduct electricity. These are 
the oxides of the metals of the earths, lime, magnesia, and others. 
They are in the full sense non-conductors when cold, having 
enormously high specific resistance, but on heating they become 
conductors. 

The Nernst Lamp is an incandescent lamp whose filament is 
made of earth oxides. These are absolutely incombustible, so that 
they can be ignited in the air, providing the condition for an 
open-air incandescent burner. 

The Glower, — The Nernst lamp filament is a straight bar of 
earth oxides and is termed the glower. To its ends are attached 
wires. The current once made to pass through the glower raises 
it to a white heat, produces light, and keeps it in the conducting 
state. The composition of the glower is not disclosed. It is said 
to be composed of the rarer earths, resembling the Welsbach gas 
mantle in composition. The standard glower for 220 volts is 
almost exactly an inch in length and 0.025 inch in diameter. It is 
formed from a putty- or dough-like mixture of the earths, by 
squeezing them through an aperture in a die. This produces a 
thread, which is dried and baked, The cuts of the Nei'nst lamp 
all show the glowers. 



THE INCANDESCENT LAMP. 



531 



Glower Terminals. — The connection of the wires with the 
glower was originally effected by winding platinum wire around 
the ends, and puttying over the ends with cement. This did not 
work very well, as the wires were apt to become partly detached, 
and thus had their contact with the glower made imperfect. The 
result of this was that the glower soon broke near the terminal, 
where the bad junction caused a concentration of heat. Another 
method is based on the reverse principle. A globule of platinun: 
at the end of each wfre / lamp termin/?:ls 

is embedded in each end ^Tr 

of the glower. Any 
shrinkage in the ma- 
terial of the glower 
•causes it to grip the 
bead still tighter. It 
cannot shrink away 
from it, as it tends to 
shrink from the wires 
wound around its ex- 
t e r i' o r. Conducting 
wires fused to the plati- 
num globules project an 
inch or two from the 
ends of the glower. The 
ends of the conducting 
wires are fastened to 
the body of the lamp by 
little aluminium plugs. 

The ends of the wires are thrust into holes in the two contact 
blocks of the lamp, and the plugs are forced into holes, wedging 
them fast. 

The glower becomes a conductor when heated to about 1300° F. 
(700° C). When cold it is a non-conductor. 

Heaters. — The glower can be heated by a match or alcohol 
flame, in order to make it conduct current. In the lamp as now 
made electric heaters are used, also shown in the cuts. These are 
of various shapes, consisting of platinum wire wound upon a 
porcelain form and imbedded in refractory paste. WJ>en the 




■ GLOVStEl^ 

FiQ. 405.— Diagram of Nernst Lamp 
Construction. 



532 



ELECTRICIANS' HANDY BOOK. 



lamp current is turned on, none can go through the cold glower, 
and a slight current only passes through the heater. It is enough 
to make it quite hot; and as it is in close proximity to the glower, 
it heats the latter, which in a few seconds begins to pass a cur- 
rent strong enough to excite a magnet, which attracts pivoted 
armatures cutting out the heater, and thereafter all the current 
goes through the glower or glowers. The heater has to heat the 

glower up to a temperature of 
about 1742° P. (950° C.) 

Ballast.— The glower is in 
series with a steadying resist- 
ance, which is called the ballast. 
The resistance of the glower di- 
minishes with increase of tem-' 
perature. The resistance of iron 
wire increases with increase of 
temperature, and the two bal- 
ance each other approximately, 
which prevents the glower burn- 
ing out. The case is analogous 
to the use of the individual re- 
sistance in a constant-potential 
arc lamp. The Nernst lamp has 
to be employed on fixed-potential 
circuits. Iron wire is selected 
for the ballast because it pos- 
sesses in a high degree the prop- 
erty of increasing in resistance with increase of temperature. It 
Is inclosed in glass tubes hermetically sealed and filled with nitro- 
gen gas, and is shown in Fig. 405. 

The Cut^Out, also shown in Fig. 405, is an electro-magnetic 
switch which opens a circuit when its magnet is excited. This 
circuit is normally closed, and only opens by the action of the 
electro-magnet as described above. The magnet winding is in 
series with the glower; the circuit which it opens contains the 
heater. 

Direct=Current Lamps.— If used on direct current, a blacken- 
ing of the glower near the negative end takes place, which causes 




Fig. 406.— Nernst Lamp Ready 
FOB. Insertion in its Socket. 



THE INCANDESCENT LAMP. 



533 



the efficiency and candle pov/er of tlie glower to fall off. Its dura- 
bility is also impaired. On alternating current this action does 
not take place, and its life is much longer. 

Vacuum Lamps. — If the glower is inclosed in a vacuum, its 
efficiency as far as the glower is concerned is increased. But 
this increase is accompanied by a very rapid rate of diminution 
of resistance with increase of temperature. This has to be met 
by a larger ballast, which reduces the efficiency. It is considered 
preferable to inclose it in a globe with access of air. This gives 





Fig. 407.— Spiral Heater and 

Single Horizontal Glower 

OF Nernst Lamp. 



Fig. 408.— Spiral Heater and 

Single Vertical Glower 

of Nernst Lamp. 



enough cooling to lighten the work of the ballast, and yet to give 
higher efficiency than in the open air. Before a glower breaks, 
the voltage rises rapidly until the rupture occurs and the lamp 
goes out. Sometimes as many as six glowers are put into one 
lamp, in which they are simultaneously ignited. The efficiency of 
such is higher than that of a single-glower lamp. 

The Efficiency of the Nernst Lamp is about double that of 
the ordinary incandescent lamp. 

The cuts, in the light of what has been said, are self-explana- 
tory. Fig. 405 shows the parts of a lamp in diagram. The 
magnet coil being inactive, the pivoted armatures are not yet 
attracted. When attracted they open the circuit at their lower 



534 



ELECTRICIANS' HANDY BOOK. 



ends, one of which is marked "silver contact" in the diagram. 
Fig. 406 shows the heaters and glowers of a lamp ready for in- 
sertion into the socket, the parts being marked. The next cuts. 
Figs. 407 and 408, show spiral heaters surrounding the glowers. 
Distribution of Light. — The diagram. Fig. 409, shows the 




80 90 

Fig. 409.— Distribution of Light From the Nernst Lamp. 



distribution of light of a Nernst lamp and of other lamps in tho 
vertical plane as by the following table: 

1. 110-volt, A. C. constant potential arc, 6.3 amp. 

2. 110-volt, D. C. constant potential arc, 4.9 amp. ' 

3. 6.6 amp. D. C. series arc, 71.6 volts. 

4. 6.6 amp. A. C. series arc, 65.4 volts. 

5. 6-glower Nernst lamp, 220 volts. 

Arc lamps — Opalescent inner and clear outer globe. 
Nernst lamp — 8-inch sand-blasted globe. 



CHAPTER XXXIL 

THE ARC LAMP. 

The Voltaic Arc. — If two rods of carbon are connected to a 
source of current and are brought into contact with each other, 
and are then separated a fraction of an inch, the current will 
continue to pass across the interval. An intense heat is produced, 
and the space between is filled with carbon vapor and minute 
particles. The heat makes the carbons very hot. As carbon is 
not a very good conductor of heat, almost all the heat concentrates 
on the ends. The arc may be produced by direct current or alter- 
nating current, which gives two divisions of the subject, direct- 
current and alternating current arc. 

Positive and Negative Carbon. — When a direct-curent arc is 
produced in the open air between two carbon pencils, both wear 
away, but do so differently. One keeps a pointed end, like a sharp- 
ened lead pencil, and is the negative carbon. The other has a 
little crater or cup formed on its end, and is the positive carbon. 
The latter gives far more light than the other. Naturally, the 
interior of the crater radiates the most light. In direct-current 
arcs the crater of the positive carbon is made to face as nearly 
as possible in the direction in which the light is to be utilized. 
Thus, for overhead lamps the positive carbon is placed uppermost, 
so that its crater radiates light to the ground. 

Strilcing the Arc. — The arc will not strike across a space filled 
with air unless a very short one. The carbons may be arranged 
to stay in contact when idle and to be pulled apart the instant 
the current starts. As they separate, the arc forms across the 
gap or space between the ends of the carbon rods. This is the 
universal way of operating arc lamps, although it can be done 
otherwise. If a spark can be made to strike across the gap, the 
arc will start over the path thus made for it. The air between 



536 ELECTRICIANS' HANDY BOOK. 

the poles is intensely heated, and is a tolerably good conductor, 
so that once the arc is established, it can be drawn out to a con- 
siderable length — greater than the striking distance of the po- 
tential utilized. 

Heat of the Arc— The resistance of the arc is not great enough 
to account for its intense heat. The positive pole is hotter, 7200*^ 
F. (4000° C.) than the negative, 5400° F. (3000° C.) to 6300° F. 
(3500° C). Counter electromotive force is set up, due to thermo- 
electric effect, or to condensation of carbon vapor, and i's equival- 
ent to resistance, and the heating effect results. The higher 
temperature of the positive pole causes it to wear away the faster. 
With alternating currents the poles wear evenly, and with almost 
flat ends if the arcs are inclosed in a glass globe so as to be partly 
protected from the air. 

Voltage Drop.— In a direct-current arc the voltage drop be- 
tween the positive carbon and the arc has been determined to be 
about 40 volts. In the arc itself a drop of 2^^ volts was observed, 
and a 2"i,^-volt drop between the arc and the negative carbon. 
These determinations are not to be considered accurate. They 
indicate the distribution of voltage, of resistance, and of light- 
giving areas or volumes with a good degree of approximation. 

Counter Electromotive Force is believed to exist in the direct- 
current electric arc, and to account for part of its apparent re- 
sistance. The cause is not certain. The different temperatures 
of the carbons producing a thermo-electric effect has been assigned 
as its cause. The alternating current arc, both of whose carbons 
are of identical temperature, exhibits apparent resistance enough 
to have counter electromotive force attributed to it. Solidifica- 
tion of carbon vapor may be the cause of its production in both 
direct and alternating current arcs. It would be possible to 
imagine the rapid volatilization and condensation of carbon 
vapor in the successive cycles of an alternating current as produc- 
ing an alternating counter electromotive force. 

The counter electromotive force for a 10-ampere 45-volt arc 
with pure carbons has been put at 35 to 39% volts. This is ap- 
proximate only. All determinations affecting the internal 
physics of the arc must from the nature of things be difficult to 
execute, and the results will generally be approximate. 



THE ARC LAMP. 537 

The Resistance of the Arc Proper has been placed at about 5 
olims per inch of length. The 10,-ampere arc, which is a standard, 
varies from 1/10 to i/o ohm in resistance, the arc length varying 
from 1/16 to % inch. Questions in which length of arc is in- 
volved are only to be valued approximately, as there is nothing 
accurate about the determination of its length. 

The resistance of the arc varies inversely in some ratio with 
the current. A heavy current diminishes the arc's resistance. 
This is the reason an arc lamp without a resistance or inductance 
for alternating currents cannot be used on parallel or constant 
potential systems. This diminishing of resistance is partly due 
to reduction of the resistance of air by heat, for the more intense 
current heats the air to a higher degree and heats more of it than 
does the smaller current. Another cause is the presence of carbon 
in the arc, probably as vapor, possibly as particles, which is in- 
creased in relative amount by greater heating. The old modifica- 
tion, which has recently been experimented with, of introducing 
alkaline earth salts or the like into the arc diminishes its resist- 
ance by supplying it with vapor of these salts or of their con- 
stituents. Increase of pressure increases the resistance. This 
applies to pure carbon arcs, and is by some thought to produce this 
effect by preventing the production of the full amount of carbon 
vapor. 

Efficiency of the Arc Light. — Of the efficiency of the arc as a 
light producer nothing can well be said beyond the comparison 
with other sources of light. The two reasons are that the arc is 
very seldom photometered, and that the absolute unit of light is 
as yet undetermined. If light is defined as that which affects 
the retina of the eye, its mechanical equivalent may be exceed- 
ingly small. What we know about odor tends to ratify this be- 
lief. An almost inconceivably small quantity of matter is re- 
quired to affect the olfactory nerves. A very minute amount 
of energy is represented in the action of light upon the optic 
nerves. 

The arc is one of the most eflicient sources of artificial light. 
The magnesium light is put next to and very close to it, and by 
modifications might be made to equal or exceed it. It is 8.66 
times as efficient as candle light, 13 times as efficient as gas light. 



538 ELECTRICIANS' HANDY BOOK. 

5.2 times as efficient as the Welsbach light. These all are so 
variable that the relative figures given are only approximations. 

The reason of its efficiency is that its heat is so intense. There 
is a possibility that there is a considerable loss by some of the 
heat producing ether waves of so short a period that they do not 
affect the optic nerve or are not visual. 

Quality of Carbons. — The nature of the carbons affects the 
efficiency. The great agent of economy is the concentration of 
heat at the ends of the carbon. Too hard a carbon is apt to be a 
relatively good conductor of heat and therefore uneconomical, 
A small diamet-er of the carbon pencil favors concentration of 
the heat at the point, and small carbons give higher results. The 
efficiency diminishes approximately in inverse ratio with the 
diameter of the carbon. A soft core in the carbons reduces the 
efficiency. In order to give better surface contact between the 
carbon clamps and the carbons, the carbon pencils are often 
copper-plated, and nickel plating has been applied. This dimin- 
ishes the light a little by improving the conductivity of the 
carbons for heat. 

Power Consumed in Arc. — A consum^ption of 480 watts is 
usual in a nominal 2000-candle-power lamp. The ratio of volts 
to amp-eres in the production of the watts expended in an arc 
lamp affects its efficiency and consequently its light. Carhart 
found that 45 volts and 10 amperes gave a maximum light of 450 
candles or 1 candle to the watt. With 8.4 amperes and 54 volts 
the maximum candle-power was doubled. There is nothing definite 
about these figures, as the size and quality of the carbons would 
affect them materially. 

Effect of Air Blast — A blast of air will blow out an arc as 
it will a candle flame. This principle is utilized in the Thomson- 
Houston alternating-current dynamo. A blast of air is there 
produced by a rotary blower, which is directed on the ends of 
the bru'shes to blow out any arc which may form in the operation 
of the machine. 

Effect of riagnet. — A pow-erful magnet deflects the arc to one 
side, and if near enough thereto and strong enough, will blow it 
out as a blast of air will. 

Voltage Drop and Arc Length. — Where the arc produced be- 



THE ARC LAMP. 539 

tween two carbons attains a certain length, it has to be increased 
in length to keep a fixed voltage. This is in line with the prop- 
erties of the arc, which makes it impossible to operate arc lamps 
on constant-potential circuits without auxiliary resistance coils. 
The resistance falls with increase of current, and the lengthening 
of the arc is necessary to bring its voltage back to its original 
figure. 

Wearing of Carbons. — With a direct current the positive car- 
bon wears away about twice as fast as the negative. The latter 
has a little accretion of carbon particles form upon it, which may 
increase its length. This amounts to nothing from the practical 
standpoint. In open arc practice, when the arc is produced in 
the open air, the accretion burns away. 

With an alternating current the wearing of the carbons, other 
things being equal, is the same for both. But when they are 
placed vertically, as they always are now, the upper carbon has 
been found to wear away about eight per cent faster than the 
lower one. This is due to the uprising currents of air and to 
gravity acting on the transfer back and forth of carbon particles. 

This uneven wearing away of the carbons affects the operation 
of arc lamps for some special purposes. Such occur in its use in 
searchlights and lighthouses, where the center of light must be 
at the level of the focus of the lens or reflector. Different feed- 
ing rates for the two carbons may be used to keep the light-giving 
gap in its proper place. 

Arc Light Carbons. — Carbons are made from a mixture of 
finely ground and ignited carbon with some carbonaceous cement- 
ing material such as pitch. They are molded into shape and 
baked for a long period at a red heat with exclusion of air. Two 
general systems of molding them are followed. 

In one grooved plates are the molds. The plates contain straight 
grooves of semi-circular section spaced equally on both plates, 
so that when the plates are laid face to face the grooves form a 
series of cylindrical molds. The composition is molded in these. 
Carbons which have been made by this or analogous methods 
sometimes show on their peripheries the mold print. 

The filled molds are heated in an oven until the mixture softens, 
when they are subjected to a hydraulic pressure of several hun- 



540 ELEGTRIGIA-NH' HANDY BOOK. 

dred tons. They are then removed, and any fin left where the 
joints between the molds Come is scraped off, and they are ready 
for baking. 

In another system the carbon composition is forced through a 
die by a hydraulic or other form of powerful press. The die 
which is at the foot of the apparatus has a circular aperture 
of the size of the carbon. The cylinder is filled with composi- 
tion which is forced out through the aperture or die. As the 
cylinder emerges it is cut into the correct lengths and the green 
carbons are baked. 

In modern practice the mixture is made into cylinders fitting 
the press cylinder. The size may be about six inches long and 
two to six inches in diameter. The cylinders are horizontal. 

To produce cored carbons a circular mandrel extends through 
the aperture of the die, and the carbon is forced out in the shape 
of a hollow cylinder. The central opening of the carbons is then 
filled with a composition, which on baking gives a softer carbon. 
The object of the cored carbon is to hold the arc in inclosed lamps 
in a central position. 

The baking of carbons has to be sufficient in temperature and 
duration to completely decompose the cementing pitch or syrup, 
and to give them good conductivity. Too much baking may make 
them too hard. Too rapid application of heat may warp them, 
and it is essential to good operation that they should be perfectly 
straight. To keep them straight during the baking and to ex- 
clude air, one method adopted is the imbedding the green car- 
bons in sand, one layer of carbons above the other in the furnace. 
From seven to fourteen days may be consumed in charging a 
furnace, baking the carbons and cooling. 

The crooked carbons are sorted out from the lot by rolling 
on a plane surface. If not too crooked, the ones thrown out by 
the rolling test are sold as seconds. From crooked carbons, short 
ones useful as bottom carbons can sometimes be cut. 

The forced carbon, as the one made by the die process is called, 
is used in inclosed arc lamps, especially in carbon feed lamps. 

The Direct=Curreiit Open Arc is the arc produced by direct 
current between two carbons in the open air. It varies in current 
from 6 to 10 amperes, and in electromotive force expended or 



THE ARC LAMP. 541 

drop from 42 to 52 volts. This refers to ordinary or standard 
size lamps, such as are in general use. Larger lamps with car- 
bons of greater diameter use more current. Some very large 
lamps have used carbons of an inch or more in diameter. 

A very large number of open-arc lamps are still in use. The 
new installations are almost universally fitted with inclosed-arc 
lamps. One of the great expenses of conducting an open-arc light 
system is the frequent trimming of the lamps. This requires 
time, which involves a labor charge. The carbons require fre- 
quent replacing as they burn out, which is another item of ex- 
pense. 

Distribution of Light in Direct- Current Open Arc. — The gas 
engineer has always tested the light given by a gas flame in the 
horizontal direction. It has never been the practice to try it at 
various angles from the horizontal. With gas this would be far 
from easy, because the gas flame must burn vertically, and the 
construction of a photometer to test its value as a light giver at 
different angles would be somewhat difficult. The electric light, 
arc as well as incandescent, is far from being as sensitive to 
change of position as is the gas flame, and by inclining the lamp 
in different positions, candle-power at various angles is deter- 
mined. This is spoken of more at length elsewhere. 

With an arc lamp with carbons end on to each other, now the 
invariable position, the follov/ing variations of candle-power to 
angle exist with direct current. 

The horizontal direction gives a low candle-power. The crater 
is screened by its edges from contributing its due share to the 
light. 

As the angle is depressed, the light given increases, until in 
the neighborhood of 40 deg. depression the greatest light is given. 
After this it decreases rather rapidly to zero directly underneath 
the lamp. 

Typical distributions of illuminating power are shown in the 
cuts. Figs. 410 to 414. The radius vectors of the curve indicate 
the relative illuminating power of the arc at the different angles 
indicated by the figures from 0° at the upper vertical to 180° 
at the lower vertical. 130° from the vertical is 40° from the 
horizontal, and this angle marks the line of greatest light. 



542 



ELECTRICIANS' HANDY BOOK. 



The lower carbon, cutting off light by its shadow, is respon- 
sible for the diminution that increases so rapidly once the 135° 
angle from the vertical is passed. 

It will be evident that it is impossible to express the value of 
an arc lamp in candle-power unless the same course is followed 
which is outlined above. It is taken in different directions, vary- 

Hissing Arc 
Over Feed 



A 



I Max. 0.P, 




600 Max. C.P. 




1250 Max. e.P. 



Extremely Long atc 
Sluggish Feed 




Figs. 410 to 414.— Distribution of Light from Open- Arc Lamp. 



ing from horizontal to vertical, thus giving eventually what 
is known as the spherical candle-power. 

Commercial Rating of Arc Lamps. — A practice has arisen of 
calling the illuminating power of an arc lamp of standard street 
size 2,000 candles. This is a 480-W'att lamp. » Another standard 
size is the 300-watt lamp, rated at 1,200 candle-power. These 
values are far in excess of the spherical candle-power. But as it 
is the earth and not the sky which is to be illuminated, the 



THE ARC LAMP. 543 

above figures are nearer the truth than they are usually supposed 
to be, if the value of the lower hemispherical candle power is 
taken. 

Hissing Arc. — On being driven too hard, or with too much 
current, the arc makes a noise. Some change occurs at this 
point, because the voltage drops suddenly 10 to 20 volts, and 
with varying current gives a straight-line characteristic for the 
voltage, the voltage remaining unchanged for wide variations of 
current. No explanation that is satisfactory has been offered for 
this phenomenon. 

Light Given by the Arc Proper. — It has already been noted 
that the positive carbon gives the most light. It gives 85 per 
cent of the light, the negative 10 per cent, and the arc proper 
only 5 per cent. 

Resistance of Short Arcs.— When the current passing between 
carbons within less than 1/25 inch of each other is increased, the 
resistance does not decrease in the same proportion, and the 
product, R I, which by Ohm's law is equal to E, increases. There- 
fore the voltage drop with such short arcs increases with increase 
of current. If this condition held for commercial arc lamps, 
they could be used on parallel circuits at constant potential with- 
out wasteful resistance coils. The length of 1/25 inch seems to 
mark a point where the voltage remains constant for a wide 
range of current. This is because in the arc of this particular 
length the resistance diminishes exactly in proportion as the cur- 
rent increases, giving a constant value to the product R I or to E. 

The Resistance of Longer Arcs on increase of current dimin- 
ishes in more rapid proportion than with short ones, so that 
as current increases, the product R I grows less. This is why 
a resistance coil for each lamp has to be employed for constant- 
potential lighting, as explained on page 55S. 

From what has been said, it follows that on constant-current 
supply the energy expended in maintaining an arc will increase 
as the length increases, and with constant length will do the 
same as the current intensity increases. On trial the increase is 
found to be a proportional one in both cases. 

Stationary State.— This is the state of normal burning of an 
arc lamp. When it starts, its constants vary until it reaches the 



544 ELECTRICIAN^ B' HANDY BOOK. 

degree of heat due to the current and distance between the car- 
bons. When this heat is reached, voltage and resistance remain 
constant as long as the length of the arc and the strength of the 
current are unchanged. In practical operation arc lamps are 
best operated in series. In this system the current is kept con- 
stant by the station management, and the regulators or lamp 
machinery maintain the distance between the carbons unchanged. 

Alternating" Current Arc. — This type of arc consumes about 
the same watts in effective reckoning as the direct-current arc 
does. The 480-watt standard divides into 15 amperes and 30 or 
35 volts. The volts are given in effective value, so the maximum 
value of the electromotive force is greater than the voltage of the 
same direct-current arc. The current value is greater in the al- 
ternating-current arc than in the direct-current arc. This com- 
pensates for the alternations, which would tend to produce flick- 
ering. 

Power Factor in Alternating= Current Arc— In the alternat- 
ing-current arc the current lags about 30° behind the electromo- 
tive force. This introduces a power factor of 85 per cent of the 
apparent watts or product of effective current and potential drop. 

Influence of Wave Form. — The efficiency of the alternating-cur- 
rent lamp is greater as its current curve avoids peaks and as its 
frequency is increased. It will be seen that the period of change 
of direction is a time when the carbon gets so little energy that 
it has to give light from its own acquired heat. The shorter 
this period, the greater is the efficiency, and therefore a high fre- 
quency is advisable for efficiency as well as for steadiness. A 
flat-tipped wave with quick or steep changes from one extreme to 
the other favors efficiency. 

Distribution of Light of Alternating= Current Arc Lamps.— 
The light from a lamp does its work generally in the lower hemi- 
sphere of its distribution; fhe light cast out horizontally and at 
all downward angles is the useful light. This distribution is 
given by the direct-current arc lamp. The cratered upper carbon, 
in which the heat is concentrated, gives most light, and its light 
is principally thrown downward, and out horizontally. The 
light of the alternating-current arc is distributed alike up and 
down, and for this reason this arc is less advantageous than the 



THE ARC LAMP. 



545 



other. A reflector is often used to reflect the upward rays down- 
ward, but its effect is small. 

Reactance Coll or Economy Coil.— Alternating-current arc 
lamps can be used on constant-potential circuit by the introduc- 
tion in the circuit of each lamp of an inductance, a coil of wire 
with laminated iron core. A single coil with several interme- 
diate connections may be used. These operate in a manner analo- 
gous to that of the individual resistance coil of a constant-poten 
tial direct-current arc lamp. They work by inductance, which is 
exceedingly economical as a reducer of current strength. It com- 
pensates in the case of constant-potential lamps for the otherwise 
low economy of the alternating-current lamp, and for its uneco- 
nomical distribution of light, as spoken of in the preceding para- 
graph. 

Efficiency of Alternating=Current Arc Lamps. — The mean 
spherical candle-power for equal watts is put at one-half that of 
the direct-current arc lamp. 

Noise. — The alternations in the current and the effects of the 
corresponding induction on the laminations of some of the parts 
caused considerable noise. In modern construction the latter 
noise is prevented by clamping fast all vibrating laminations of 
iron, and by the use of springs and India-rubber supports for 
such parts, so as to prevent anything like sounding-board action. 
The application of the inclosed-arc principle operates to greatly 
diminish the hum of the arc. 

Duration of Carbons. — The alternating-current inclosed-arc 
lamp with a 6-inch lower and 9%-inch upper carbon burns about 
80 hours before the carbons need renewal. The direct-current in- 
closed-arc lamp may run 100 to 150 hours before the carbons 
need changing. This is to be compared with 8 to 10 hours' dura- 
tion for open-arc lamps. 

Length of Arc. — The alternating-current arc is in practice 
about % inch with a 6-ampere current and 70 to 75 volts. This 
is quite different from the direct-current factors of working. 

Inclosed- Arc Lamps. — The original arc lamp of the early days 
of electricity, with charcoal electrodes made conducting by im- 
pregnation with mercury, was of very short duration as regarded 
its carbons. It was only experimental, was actuated by a primary 



546 JjJLECTRICIANS' HANDY BOOK. 

battery which soon expended itself, and awaited the development 
of some cheap source of electricity to become practical. 

When the modern dynamo gave large quantities of electric en- 
ergy, many forms of arc lamp were devised, depending for the 
durability of their carbons on the composition of the same. These 
were made hard and relatively incombustible, but in the intense 
heat of the arc they burned away quite rapidly and had to be 
frequently replaced. On every replacement a stump of more or 
less considerable length was lost and thrown away. 

About 1882 attempts were made to follow in the wake of the 
incandescent lamp, and to inclose the arc in an air-tight globe. 
In 1894 successful inclosed-arc lamps were produced, and now 
the movement is for their universal use. 

It is evident that an hermetically-sealed globe is almost an 
impossibility for an arc lamp. The carbons are certain to be re- 
duced as the lamp burns, irrespective of combustion. The arc 
wears away the carbons mechanically by its transfer of carbon 
particles from one carbon to the other. The problem of inclosing 
and protecting the carbons is solved by using an approximately 
tight globe. The carbon is fed through a hole in the top, which 
it almost fills. The globe is otherwise closed. A very little air 
gets in by diffusion, but the duration of the carbons is increased 
very greatly. 

On standing idle, the globe slowly fills with air. On starting the 
arc, combustion of the carbon begins, and in a few minutes the 
oxygen in the globe is exhausted, being replaced by carbonic-oxide 
and carbonic-acid gases, and the wasting of the carbons is now 
mechanical for the most part. 

The Action of the Inclosed Arc is to transport carbon particles 
from the positive carbon to the negative. These particles im- 
pinging on the hot negative carbon stick there, and tend to form 
a little lump upon it. The positive carbon wears away, with a 
slight tendency to become concave or a very little hollowed at the 
end. The negative has the opposite tendency, becoming slightly 
rounded. If the carbons are started with the usual pointed ends, 
they soon become almost flat-ended. 

The object being to preserve the shape of the carbon ends, the 
more or less irregular deposit of carbon particles on the negative 



THE ARC LAWIP. 547 

electrode is a disadvantage. The carbon particles do not all de- 
posit on the negative, but also tend to form a blackish coating on 
the glass. If the globe were hermetically sealed, the glass would 
inevitably blacken. Recourse is had to the air as a cleaning 
agent. Enough finds its way into the globe to burn up the car- 
bon particles and vapor and prevent it from forming the deposits 
on the glass and on the negative carbon. The present successful 
form of inclosed-arc lamp is the product of years of experimenta- 
tion and gradual development. 

The General Electric Company inclosed-arc lamps have a com- 
bined globe and lower carbon holder. The lower carbon is held 
stationary, all the feed being done by the upper carbon. This 
feature enables the trimmer to remove the lower carbon and globe 
together and replace them by a clean globe and new lower carbon. 
The globe removed can be returned to the station for cleaning. 
The inclosing globe is comparatively small, Q% inches high by 3 
inches diameter. A small passage several inches long in the 
cap connects the space inside the globe with the air. The idea 
is to have the passage act as a gas chamber to prevent the direct 
access of air. 

Globe and Carbon Holder.— This is shown in Fig. 415. B is the 
globe holder which is seen rising from it, and in its center are 
shown the lower carbon and the lower end of the upper carbon. 
The head of the screw for fastening the lower carbon faces the 
reader. A is the holder for the outer globe, which is held from 
shaking by the spring & 6, which goes inside it. The frame carry- 
ing it is drawn down. When the lamp is in use, the frame is 
pushed up, the clamp C enters the slot at D, and by turning the 
clamp through 90° all is secured. 

Inclosed=Arc Lamp Carbons.— In inclosed-arc lamps of stand- 
ard size, %rinch carbons are used. The upper one is for direct- 
current lamps 12 inches and the lower one 5 inches long. The 
upper one wearing away twice as fast as the lower one, becomes 
too short after long burning. Before it* loses more than half its 
length, the lamp has to be trimmed. This is not only necessary 
for the replacement of carbons, but also for cleaning the small 
globe. A certain amount of carbon dust and ashes collects in 
the inclosing globe, which has to be cleaned. 



548 ELECTRICIANS' HANDY BOOK. 

The short lower and negative carbon becomes reduced to a mere 
stump, and can without much waste be thrown away. The upper 
carbon, about half its former length, is preserved and is cut 
down to the standard length of 5 inches, and is used as the lower 
carbon. 

A lamp of this type burns for 125 hours or for 10 or 12 nights 
without trimming. 

One characteristic of inclosed arcs affects the shape of the 
carbons. They burn with approximately flat ends. This undoubt- 
edly hurts their efficiency by screening off the incipient crater or 
hottest point on the positive. The flat opposing negative and the 
projecting area of the positive operate to produce this screening. 

On 110-volt constant-potential circuits a lamp will take 80 volts; 
on 120-volt circuits it will take 85 volts. The remainder is taken 
up and lost in the resistance coils which are used on constant-po- 
tential systems. 

The Clutch. — The development of arc lamps was marked by the 
most important application of the clutch to the carbon feed. The 
cut. Fig. 416, shows one of the original forms, the old Brush 
clutch. It is designed as shown to feed two carbons. It consists 
of a flat plate W with a hole slightly larger than the rod or carbon 
R which passes through it. "When its end is lifted by the mech- 
anism operating K, the plate binds or grips the rod and raises it. 
When the end is lowered, rod and clutch descend together, the 
clutch not losing its grip until the outer free end is arrested in 
its descent. The clutch is then said to trip. As it approaches the 
horizontal position on being tripped, the grip ceases, and the rod 
descends through it. 

In Fig. 417 is shown a modern clutch. When the lever F is 
raised or as long as the weight of the carbon is sustained by it, 
the upper end C of the shoe is pressed against the carbon or earn 
bon rod A, and grips it between itself and the upper end of D. 
As tbe carbon burns and is fed down a little, the tripping piece 
E touches the tripping platform G, and the lever F descending, 
the grip opens and the carbon can drop down. The lifting posi- 
tion is shown in the left-hand figure, and the releasing position 
in the right-hand figure. A still simpler clutch is shown in Fig. 
418. It is used in the General Electric Company's arc lamps. 



THE ABC LAMP. 



549 



Tripping Platform. —This name is given to the little platform 
or plate which the clutch comes in contact with on its descent, 
and contact with which trips it, and causes it to relax or lose its 
grip upon the rod. In Fig. 417 a tripping platform is seen at G. 




Fig. 415.— GriiOBE Holder of 
iNCiiOSED-ARC Lamp. 



Fig. 417— Arc Lamp 
C1.UICH. 



It is also shown in Fig. 422 directly above the lamp globes and 
below the clutches. 

Carbon=Feed Lamps.— The clutch is used for almost all com- 
mercial lamps. It may grip a brass rod or tube to whose lower 
end the carbon pencil is secured. The advantage of this arrange- 
ment is that the clutch has always the same cylinder to act upon. 
In many lamps the clutch grips the upper carbon directly. Such 



550 



ELECTRICIANS' HANDY BOOK. 



Fig. 4ia— Aro Lamp Clutch. 



lamps are said to have a carbon feed. The carbons for such must 
be of uniform shape, and but a very slight variation in diameter 
is admissible. 

Concentric Magnets.— In some lamps a single magnet coil is 
used, placed directly in the axis of the lamp. A plunger works 

up and down within the coil 
and operates the feeding 
mechanism. In other types 
of lamps the magnet coils 
are placed to one side of the 
axis. In Fig. 419 is shown 
the type used in some of the 
General Electric Company's 
lamps, a U-shaped magnet 
with double-plunger arma- 
ture. 

Dash Pots. — A dash pot. 
Fig. 420, is a cylinder with 
a piston. Owing to the slow 
escape and ingress of air, 
the piston cannot move rap- 
idly up or down, although it 
fs devoid of friction as far 
as possible. Thus, it is quite 
free to take any position, 
but is not free to do so rap- 
idly. The piston is attached 
to one of the armature parts in arc lamps, so as to rise and fall 
with the armature. While entirely without effect upon the posi- 
tion ultimately taken by the armature, it prevents all sudden 
movements and secures steady carbon feed. 

Carbon Holders.— The lower carbon does not move, and is set 
into a socket, as shown in Fig. 415. This may have a setscrew 
to retain the carbon firmly in position. An upper carbon holder 
is often a short tube. Fig. 421, whose lower end is slotted and 
springs over the upper end of the lower carbon; the wire from the 
line connects to the top of this holder. The holder slides up and 
down in a long vertical tube in the axis of the lamp. Its mo- 




FiG. 419.— Arc Lamp Magnet With 
Double-Plunger Armature. 



THE ARC LAMP. 



551 



Fig. 420.— Dash Pot. 



tions are governed by the magnets and clutch mechanism. In the 
diagram, Fig. 422, the tube is seen in a vertical position directly- 
over the carbons, and within it is seen the carbon holder with 
the leading-in wire coiled in the tube above it. 

Constant=Current or Series Arc Lamps.— In operating arc 
lamps on series, a constant current is forced through the line. 
The length of the arc cannot therefore be regulated by the current 
in series, as the latter is invariable. The carbons in a single 
lamp may be drawn so far apart as to greatly increase the re- 
sistance and disturb the working of the entire series of lamps. 
This possible trouble has to be pro- 
vided for also in constant-current 
lamps. 

Two magnets are used to operate 
the clutch. One magnet is in series 
with the lamp, and when the current 
is turned on, the clutch is raised, lift- 
ing the upper carbon, which when the 
lamp is idle rests upon the lower one, 
and causes the arc to strike. This 
ends the functions of the series mag- 
net until the next period of lighting 
comes. 

A second magnet is placed in .par- 
allel with the arc. As the arc in- 
creases in length, the resistance of the arc also increases, and 
more current is shunted through the shunt magnet. This mag- 
net is so connected to the clutch that as it attracts its arma- 
ture and the latter rises, the clutch descends, thus shortening the 
arc. 

If for any cause the arc should become too long, so as to re- 
quire two or three more volts for its maintenance than proper, 
the mechanism closes a cut-out, which operates by closing a cir- 
cuit in parallel with the lamp. If the carbons descend, and the 
ends come in contact because the clutch trips and refuses to act, 
the cut-out also closes. Thus the cut-out becomes operative at 
either extreme. 

The diagram. Fig. 422, illustrates the action. It shows the lamp 




Fig. 431.— Copper Carbon 
Holder. 



552 



ELECTRICIANS' HANDY BOOK. 



" ^ zifc. 



inactive, the carbons in contact, and the cut-out closed. If cur- 
rent is turned on, it goes through the cut-out. In series with 
the cut-out is a coil which provides the starting resistance. Its 
resistance shunts sufficient current through the series magnet 
to cause It to attract its armature and raise the clutch. This sep- 
arates the carbons, the arc 
strikes, and current is shunt- 
ed through the shunt mag- 
net. This at once begins to 
regulate the length of the 
arc. 

The armatures of the 
shunt and series magnets 
operate a rocker arm which 
is pivoted between the mag- 
nets, so that the series and 
shunt magnet have reverse 
effects on the movable 
upper carbon. As the 
shunt-magnet armature is 
drawn up, the clutch de- 
scends, owing to the action 
of the rocker arms, and the 
reverse action takes place 
when the shunt-magnet ar- 
mature descends. In this 
way the increase of arc 
length shunting more cur- 
rent through the shunt mag- 
net causes the clutch to de- 
scend and the arc shortens. 
The dash-pot is shown to the left of the central tube above the 
rocker arm. Immediately below the clutch is the tripping plat- 
form, seen extending over the top of the globe. 

Adjusting Weight.— This slides back and forth upon the rocker 
arm attached to the two armature rods. This is fastened in any 
desired position by a setscrew. For variations in current exceed- 
ing 0.2 ampere above or below the rated current of the lamp. 




STARTING 
RESISTANCE 



!FiG. 433.— Diagram of Conptant- 

CuBRENT Series Arc Lamp 

Mechanism. 



THE ARC LAMP. 



553 



the weight must be shifted. Moving the weight toward the clutch 
rod reduces arc voltage, and moving it away increases arc voltage. 

Fig. 423 shows the lamp with the cover removed from the mech- 
anism. The parts can be identified by 
the diagram, Fig. 422. 

Action of an Arc Lamp on a Constant => 
Potential Circuit. — The resistance of the 
arc d-ecreases as the current increases, 
and vice versa. Therefore on a constant- 
potential circuit, where the current is 
practically unlimited, an arc lamp can- 
not be used without auxiliary apparatus. 
The resistance coil in the case of the 
direct-current arc lamp, and the induc- 
tance coil in the case of the alternating- 
current lamp, are the auxiliary apparatus 
preventing this action. 

Action of the Resistance Coil in a 
Constant "Potential Arc Lamp. — A mo- 
mentary increase in the current through 
a lamp without a coil would lower its re- 
sistance so that tco much current would 
pass, and the current would increase until 
some damage would ensue or until a fuse 
would blow out. But a fixed resistance in 
series with the lamp prevents this trouble. 
By Ohm's law, E = RI, with fixed resist- 
ance the drop required to force a current 
through the resistance will increase or de- 
crease in proportion to the current. The 
drop of potential expended on the lamp 
alone is a fixed amount, that of the po- 
tential of the system minus the drop ex- 
pended on the resistance coil. The moment the current increases 
in the lamp, the drop in the resistance coil is increased and that in 
the lamp is diminished. This reduction of drop cuts down the cur- 
rent again to its proper amount. 
• A momentary decrease in the current, on the other hand, in- 




FtG. 423.— Constant- 
Current Series Arc 
Lamp. 



554 ELECTRICIANS' HANDY BOOK. 

creases the resistance of the lamp, which cuts down the current 
still further, and the lamp may be quite extinguished if without 
a series resistance. But with a resistance in series the action 
converse to that just described takes place. A reduction of cur- 
rent through the lamp and resistance coil can only be due to an 
increased resistance in the lamp. This decreases the drop in 
voltage due to the resistance coil; and as the dynamo maintains 
a constant voltage, the drop at the lamp is increased. This oper- 
ates to give inore current to the lamp, compensating for its in- 
crease in resistance. 

The reactance coil in series with the alternating-current lamp 
acts fn the same way, except that reactance of induction plays the 
principal role in steadying the lamp, resistance being quite sec- 
ondary. 

An additional regulating action of the series resistance may 
be sought for in fts variations in temperature. As more cur- 
rent passes, it gets hotter and increases in resistance. This is 
exactly what is wanted; but whether this action is ever sufficient 
in extent to play any part in the actual regulation is problematical 
in most cases. 

A standard potential for constant-potential systems is 110 volts. 
This, of course, varies considerably in different parts of a district, 
but it gives a basis for parallel circuit arc lighting. Forty to 
fifty volts are the drop for a commercial open-arc lamp. Two in 
series with a steadying resistance will meet the voltage of the 
incandescent system. This has become a general method of dis- 
posing of them. They take some ten amperes of current, so that 
each group of two in series represents fn current consumption 
twenty incandescent lamps in parallel. 

The ParaIlel=Circuit System of Electric Supply is very ex- 
travagant in first cost of installation. A district could have its 
illumination supplied by incandescent lamps in series of twenty 
or more through a network of comparatively small wires. Roughly 
speaking, one extreme would be the case where the copper mains 
which would supply the lamps would be of but one-twentieth the 
size of those inquired on parallel circuit for the same lamps. 

First cost of installation is capitalization, and interest has to 
be paid upon it, so that heavy copper mains and large current 



THE ARC LAMP. 



555 



machines are a source of annual expense just as much as coal 
consumption. An arc lamp gives far more light per unit of power 
than an incandescent lamp. Placed in parallel circuit it exacts 
large mains, and the resistance in series consumes energy. 
■ The series connection is the ideal system for arc lamps. They 
are used for continuous or periodic illumination, are not supposed 
to be lighted and extinguished by con- 
sumers, and the use of them on parallel 
circuit is a concession to an existing state 
of things only. No engineer would pri- 
marily establish a parallel system of arc 
lighting. 

Constant=Potential Arc Lamps. — This 
class of arc lamp operates on constant- 
potential circuits, and its regulating mag- 
net is operated by variations in the cur- 
rent. An increase of current causes the 
magnet to lift its armature, and thereby 
to lift the upper carbon. This increases 
the length of the arc and its resistance 
and reduces the current. A diminution 
of current permits the magnet armature 
to descend, the upper carbon descends 
with it, and the arc fs shortened. This 
reduces the resistance of the arc and in- 
creases the current. The increase of cur- 
rent arrests the downward movement of 
the armature, and may cause it to rise a 
little. These converse actions keep the 
length of the arc approximately the 
same. 

The diagram, Fig. 424, shows the principle of construction of a 
constant-potential arc lamp of the General Electric Company. 
The one illustrated is an alternating-current lamp. For the pur- 
poses of this description the principal difference between it and a 
direct-current lamp is the use of a reactive coil instead of a 
resistance coil. The current enters by a binding post, passes 
through the reactance coil, the lower carbon arc, and upper car- 




Fig. 424.— Diagram op 
Constant Potential 
Alternating -Current 
Arc Lamp Mechanism. 



S56 



ELECTRICIANS' HANDY BOOK. 



bon in the order named. It then passes through the magnet coils 
and out on the line. The armature is of double-plunger type, with 
the lower end of the plungers connected by a cross bar which 
carries a downwardly projecting rod at its center, which oper- 
ates the clutch as shown. Immediately below the clutch is a trip- 
ping platform. When the clutch strikes this it trips, and the 
carbon drops a little. Another distinction between the constant 
current lamp and the constant potential lamp is that the latter 
has only one regulating magnet, which is in series with the arc. 

The reactance coil is shown in horizontal diagram above the 
lamp. The lettered places indicate points of connection for the 





Fig. 435.— Reactance Coiij fob 
Constant Potential Alteb- 

NATING-CUBBENT AbC LaMP. 



Fig. 426.— Resistance Coil, 

FOB Constant Potential 

Direct -Cubrent Arc Lamp. 



wires. The wire T, the right-hand one in the cut, is always con- 
nected to point A or B'. The wire S, over the top of the lamp, 
is connected to any of the other points according to the voltage 
on the circuit and the frequency of the circuit. The arc voltage 
is taken at 70 to 73 volts. For 60 cycles and 104 volts on the line, 
S should be connected probably to J; for 125 cycles and 104 volts, 
to F. To increase arc voltage fewer coil divisions must be 
brought into series. Thus, changing the wire S from M to L or 
to K increases the voltage of the arc by cutting out part of the 
reactance of tlie coil. 

The direct-current lamp is of the same construction, except that 
it contains no reactance coil, but a resistance coil wound upon a 
grooved porcelain block occupies the same place. A sliding con- 
tact arranged in a groove shown on the side of the porcelain 



THE ARC LAMP. 



557 



block enables the resistance to be regulated by rheostat action. 

Fig. 425 shows the reactance coil, and Fig. 426 the porcelain 
block for resistance coil. The groove on the side receives the 





Fig. 427.— Constant Poten- 
tial, Alternating-Cub- 
RENT Arc Lamp. 



Fig. 428.- Constant Poten- 
tial Direct-Current 
Arc Lamp. 



sliding contact piece used to cut out resistance as desired. The 
alternating-current lamp is shown in Fig. 427, and the direct- 
current lamp in Fig. 428. 

In both types of lamp the arc is liable to travel from side to 
side of the space between the carbons. The effect on the dis- 
tribution of light is quite different in the inclosed and open arc 



558 



ELECTRICIANS' HANDY BOOK. 



lamps, and is illustrated in Figs. 429 to 434. The distribution of 
light from the open arc lamp with central and side arc is shown m 







Ftgs. 439 TO 431.— Distribution ov 

Light in Direct- Current 

Open- Arc Lamps. 



Figs. 43i to 434.— Distribution I 
OP Light in Direct-Current 
Inclosed- Arc Lamps. 



Figs. 429 to 431. The crater in the upper carbon is so displaced 
by the migrations of the arc as to make a great diilerence in 
the amount of light given on the side where the arc is, compared 
with that given by the other side. Figs. 432 to 434 show the ef- 



THE ARC LAMP. 559 

feet of the migration of the arc in direct-current inclosed-arc 
lamps. As only a slight crater forms in the carbons of this type 
of lamp, the unevenness of distribution of light due to shifting 
of the arc is very slight. 

Management of Inclosed=Arc Carbons. — To get the longest 
life out of the carbons, the following rules should be observed. 
The lamp should not be run on a circuit of frequency or voltage 
different from that for which the lamp was adjusted. A lamp 
when burning should have at least 100 volts drop at the arc. The 
carbons in inclosed-arc lamps are separated by twice the interval 
which obtains in the open-arc lamps. The inclosing globe must 
fit perfectly. Its upper edge must make a virtually air-tight 
joint with the cap. The mechanism must work freely, so as to 
insure correct feed. The old upper carbons can be cut to proper 
length if too long, and used as lower carbons. Carbons should 
not be used of length greater than that specified for the lamp. 

Adjusting Lamps,— Lamps are usually sent out adjusted for 
the voltage or current which the purchaser has specified in his 
order. A variation of a quarter of an ampere above or below 
the rated current calls for adjustment. In the General Electric 
Company's lamps a weight is sometimes mounted on the working 
lever. This weight can be shifted so as to adjust the lamp for 
different currents. Moving this weight toward the clutch rod 
reduces the voltage or drop at the arc; moving it in the other 
direction increases it, as it acts to pull the carbons apart. 

The Inclosing Globes. — The directions for installing lamps is- 
sued by the manufacturing company sometimes specify that the 
lamps should not be started without the small inclosing globe 
being in place. This instruction should be rigorously followed. 
The inclosing globe is as much a part of the lamp as the carbons 
are. Not only the rate of consumption of carbons is reduced by 
the presence of the globe, but the carbon ends take a different 
shape. The reduction in consumption of carbons is important 
as an economy in supplies, and because it diminishes the labor 
bill for trimming. The inclosing globe is subjected to strong 
heat. It must not be clamped so tight as to break for lack of 
room to expand. The hole for the upper carbon must be a good 
but perfectly loose fit. The little air which works in through it 



560 ELECTRICIANS' HANDY BOOK. 

is rather a benefit than otherwise, as it tends to keep the lamp 
cleaner. 
Negative and Positive Connections in Inclosed=Arc Lamps — 

If a direct-current arc lamp is to be installed, the upper carbon 
must be connected to the positive terminal of the line. If there 
is any doubt about the connections, the current may be turned on 
for a few minutes and then turned off. If properly connected, the 
upper carbon will be the hotter, and consequently will remain 
red hot longer than the lower one will. If improperly connected, 
the lower carbon will be the hotter. In such case reverse the con- 
nections. 

Putting a Lamp Into Service. — After unpacking a new lamp re- 
move the upper casing. This is sometimes secured by a bayonet 
joint, sometimes by screws. Sometimes wedges and packing are 
used for safety in shipping. Such will be seen inserted in the 
machinery, if present. Remove them carefully, brush out the 
machinery if necessary, examine it for loose parts, and see that 
the movable parts work freely. When all is in order, replace 
the casing. Sometimes lamps are shipped with the lower carbon 
holder and its rod removed from the lamp. If so, it must be 
put into place. Care must be taken in doing this to center ac- 
curately the lower carbon. This is effected by putting the lower 
carbon rod in its right position. Then perfectly straight carbons 
should be used. If they do not come in line, the lower carbon 
holder may in some lamps be used to rectify their position by 
twisting. 

Oil. — Do not oil the dash pot or other mechanism of an arc 
lamp. Its parts are so exposed that lubrication is inadvisable. 

Clutcli Stop Adjustment. — The clutch stop should be so ad- 
justed that with the carbon of smallest allowable diameter the 
upward movement of the clutch is arrested when the armature is 
within one-eighth to one-quarter inch of the magnet pole faces. 

Cut=Out. — The cut-out is adjusted to close when the stem of 
the clutch is about one-sixteenth inch below the tripping point. 
The lamp should with this adjustment cut out when the voltage 
is two or three volts above the feeding voltage. 

Carbons for IncIosed=Arc Lamp.— For satisfactory operation 
of an inclosed-arc lamp, one cored and one solid carbon should 



THE ARC LAMP. 561 

be used. In ordering, half of the order should be for solid and 
half for cored carbons. They may all be of the same length, say 
twelve inches. When the lamps are started, the lower carbons 
can be got by cutting 12-inch carbons into pieces. Afterward the 
partly-burned upper 3arbons will act as lower carbons. The car- 
bons must be smooth and of even diameter. The upper one is 
supposed to act almost as a stopper for the upper hole in the 
inclosing globe's metallic cap. Any friction at this point will 
interfere with the feed of the upper carbon and may put the lamp 
out. 

To Carbon a Lamp.— The following directions are given by the 
General Electric Company for their series inclosed-arc lamps. 
Be sure that the current is switched off. Hold the inclosing globe 
firmly and swing the bail to one side after pulling down on it. 
The globe will come off. Loosen the setscrew and remove the 
lower carbon. Remove the upper carbon, and put in a new one,, 
inserting it in the spring carbon holder of the upper carbon 
tube. Put a lower carbon of proper length in the lower holder, 
and secure it with the thumbscrew. Replace the inclosing globe, 
being careful to set the upper edge squarely against the finished 
surface of the cap, so as to exclude the air from the arc. Secure 
the globe by placing the supporting ring of the bail around the 
projection on the bottom of the globe. To insure proper electrical 
connection to the upper carbon, it must be well inserted in the 
spring carbon holder on the inside of the carbon tube. The 
insertion of the carbons into the holders is facilitated by their 
having beveled ends. The inclosing globe should be cleaned at the 
station periodically, or the dirt which collects on its inner sur- 
face will reduce the light. The above directions have to be modi- 
fied for lamps with inclosing globes of other type. The modifica- 
tions are obvious on inspection of the lamp. 

Lamps Without flechanism. The Jablochkoff Candle. —At 
one time the efforts of inventors were directed to the end of 
producing an arc lamp without mechanism, but all such have 
practically gone out of use. The Jablochkoff candle, illustrated in 
Fig. 435, had very extensive use at one time. It consisted of two 
parallel rods of carbon separated by an insulating material, such 
as gypsum. They were used necessarily with an alternating cur- 



562 



ELECTRICIANS' HANDY BOOK. 



rent. A small bit of carbon was laid across the top to connect 
tbe carbons. This enabled the current to start, and in a few 
seconds the carbon slip burned away and the arc was formed. 
In the cut dd are the line connections, & is a spring keeping 
pressure upon the socket holding the base a of the candle. Once 
the arc was formed, it was supposed to continue until the candle 
burned out. If the arc went out, it would not form again. 

The Wallace Lamp, an American invention, is deserving of 
notice, although it was never much used. The carbons were In 

the form of two rectangular plates. 
By regulating mechanism they were 
kept edge to edge within a fraction 
of an inch of each other. The edges 
were sensibly parallel to each other, 
but inevitably one place would mark a 
slightly closer approximation of the 
carbons. Here the arc sprang across, 
and as it burned, increasing the dis- 
tance, it shifted a little, and eventually 
traveled the whole length, several 
inches in extent, of the edges of the 
carbon plates. As the distance be- 
tween the edges increased, the upper 
plate was fed down so as to diminish it. 
The Sun Lamp had two inclined 
rods of carbon occupying a position 
like that of the two arms of the letter V. They descended through 
holes in a block of refractory material by their own weight. 

Open -Air Incandescence. — One modification of the true arc 
lamp has disappeared from the field. Open-air incandescence was 
the name given to the principle on which this class of lamps oper- 
ated. This principle utilized the loose contact between a carbon 
point resting on a carbon surface as the seat of incandescence. 
This secured a simple gravity feed, and to a considerable extent 
got rid. of mechanism. 

Gradually all these lamps died out, and at the present time arc- 
lamp lighting is fast settling down into the use of the inclosed- 
arc lamp with positive downward feed of the upper carbon. 




Fig. 435. 



-The Jablochkoff 

Candle. 



CHAPTER XXXIII. 

PHOTOMETRY. 

Standards of Illuminating Power.— The light given by a source 
of illumination, such as a gas flame, oil lamp, or electric lamp, 
has in the existing state of science to be referred to and meas- 
ured by some standard. The usual standard in this country is 
the candle. This is a sperm candle burning 120 grains per hour. 

Many other units of illuminating power have been proposed, 
and in other countries they have been adopted to a greater or 
less extent. A number of the more prominent are summarized 
below, with their relative values. 

The light given by a lamp is called indifferently its illumin- 
ating power or its candle power. The latter term does not apply 
to French practice, where the Carcel lamp (Bee Carcel) is the 
standard. 

Principle of the Photometer. — The principle on which the test- 
ing of lamps for candle-power is based is the following. The 
source of light is assumed to be a point. As the distance of the 
observer from it is increased, he receives less light. The degree 
of light received is dependent on the area over which its effect 
is spread, and like all radiations its intensity varies inversely 
with the square of the distance. 

The cut, Fig. 436, shows this clearly. The larger area has 
distributed over its surface the exact amount of light which 
lights the smaller area. One is twice as far removed from the 
source of light as is the other, and its area is four times as great. 
Therefore, a portion of the area, of the distant surface equal in 
area to the nearer one receives one-quarter the amount of light, 
because it is at double the distance. 

Suppose two lights are placed at a distance of 90 inches from 
each other, and a screen is placed at a point on the line connect' 



564 



ELECTRICIANS' HANDY BOOK. 



ing them where it will receive an equal amount of light from 
each. Suppose that this point is 60 inches from one light and 
consequently 30 inches from the other. The ratio of 60 to 30 is as 
2 is to 1. As the light given varies inversely with the square of 
the distance, it follows that the nearer light is of one-quarter the 
power of the distant one. 

Bar Photometer. — ^The above is the principle of the bar photo- 
meter, the instrument universally used for testing the candle- 
power of lamps, as well as of the shadow and other less used ap- 
paratus. 




¥iQ. 436.— Law of the Inverse Squares. 



Photometric Screens. — A screen is used to determine the point 
on the bar at which an equal amount of light is received from 
both sources. Several devices have been employed or suggested 
for this purpose. 

The Bunsen Disk. — The Bunsen disk is founded on the follow- 
ing principle. If a spot upon a sheet of paper be treated with 
grease, it will become more translucent and less reflective than 
it was before. Therefore, if seen by transmitted light, if held 
between the observer and a candle, for instance, it will appear 
lighter in color than the rest of the paper. If light is caused to 
shine upon it, then the spot will appear darker than the rest of 
the paper, because it does not reflect light so well. 

If such a piece of paper is held between two sources of light 
and receives the same amount of light from each, the spot will 



PHOTOMETRY. 



565 



tend to disappear. It may not disappear completely, but the posi- 
tion of greatest faintness is easily found with considerable ac- 
curacy. 

The disk is made of rather heavy white paper, and the spot in 
the center is made by melting paraffin wax into the paper. Any 
kind of greasy matter will do as an expedient for temporary pur- 
poses. A hot bit of wire will answer for melting it into the 
paper. The translucent spot should be about an inch in diameter. 
Sometimes the spot in the center is the untouched paper, and 
the paraffin is melted in a ring surrounding it. 

The Leeson Disk.— This screen is of the simplest description 
also. A star is cut out of a piece of 
heavy note paper. It is laid between 
two pieces of thin note paper. In use 
the screen is moved to such a posi- 
tion that the star appears equally 
bright on both sides of the disk. 

flounting the Disks. — The disk or 
screen should be three or four inches 
in diameter. It is mounted on a block 
of wood which slides upon the bar. 
The observer then looks first at one 
side and then at the other, shift- 
ing it back and forth until the spot 
nearly disappears. It is then receiving 

the same amount of light from both sources, and the reading on 
the bar gives the relative intensity of the lights. Sometimes the 
disk as shown in Fig. 437 is mounted between two mirrors. A B 
is the frame carrying the disk, M N and M' N' are the two mir- 
rors. This enables the observer to see both sides of the disk 
without moving his head. A disk mounted in this way between 
mirrors is often carried in a little car which runs along the bar. 
The center m of the disk should be on the level of the two- 
lights which are being compared, and directly between them. 

The Lummer=Brodluni Screen.— In this screen the observations 
are made with a single eye, eliminating it is claimed any chance 
of error due to unequal sensibility of the two eyes. The diagram. 
Fig. 438, represents the horizontal plan of the apparatus. It is 




Fig 437.— The Bunsbn Disk 

Mounted Between Two 

Mirrors. 



566 



ELECT RIG I AN 8' HANDY BOOK. 



supposed to be mounted on the photometer bar. C indicates the 
standard lamp, X the light which is being tested. S is an opaque 
white screen of plaster of Paris; both sides are illuminated, one 
by each light, C or X. At M and N are mirrors which reflect the 
light to the prisms, the beams falling normally or perpendicularly 
upon the face of the prism receiving it. Each prism has a spherical 




Fig. 438.— Lummer-Brodlum Photometer Screen. 



face, and a circle is ground upon the center of each face, one circle 
being larger than the other. When placed in contact, flat side 
against flat side, there is a circle of contact, surrounded by the 
outer parts of the larger circle, which is not in contact with the 
other prism. Light reflected from the mirror N passes through 
the circle of contact to the observer's eye at the end O of the 
sighting tube. The circle of contact shows the degree of illu- 
mination of the side of the screen S facing C and lighted by it. 
The light from the side of the screen S, due to X, reflected from 



PHOTOMETRY. 



567 



the mirror N, goes to the double prism also. The portion of the 
beam which impinges on the outer flat circle is reflected to the 
observer's eye at O. The observer therefore sees a circle through 
which light from C passes, surrounded by a circle from which 
light from the screen S due to X is reflected. If the screen is 
moved back and forth upon the bar, a point will be reached when 
each side of the screen will receive the same intensity of light. 
At this point the central circle and outer circle will appear 
of equal brightness. The back of the outer circle is blackened, 
and total reflection of the light falling on it ensues. 

It is estimated that the mean error of setting this screen does 
not exceed five per cent, and that it is four or five times as ac- 
curate as the ordinary Bunsen or Leeson disks. 




Ftg. 439.— The Bar or Btjnsen Photometer. 



"The Standard English Candle.— This, which is the American 
standard also, is a sperm candle burning 120 grains of sperm 
per hour. It is the commercial article made of a mixture of v*/^ax 
and sperm, and with a plaited wick. When in good condition the 
wick should bend over and have a red end. If it burns more 
than five per cent too much or too little, the readings are to 
be distrusted. The standard candle in hot weather is apt to burn 
too much sperm, and give too high a value to the lamp which is 
being tested. This is sometimes overcome by putting the can- 
dles on ice for an hour before they are used. At best, it is so 
very poor a standard that the wonder is that it has so long been 
used. 

The Apparatus,— The general disposition of a photometer is 
shown in the cut. Fig. 439. In it are shown the divided bar. 



56S ELECTRICIANS' HANDY BOOK. 

with an electric lamp to be tested at one end of it and the candles 
at the other. The box holding the disk and mirrors runs upon 
wheels along the bar. The apparatus is contained in a room with 
blackened walls. A curtain may be used to further inclose it. 

Calculating the Scale of the Bar. — It would be a simple 
matter to use a bar divided into inches and fractions of inches. 
Then by placing the screen at a distance where it would be 
equally illuminated on both sides, the distances of the two lights 
from it could be squared, and their inverse ratio would give the 
relative illuminating power as above. It would be more conve- 
nient to have the bar so divided as to give by its direct reading 
the relative value of the two lamps. This system of dividing is 
frequently followed. It may be done by the following process: 

Let 1 = value of standard light at one end of bar. 

Let V =■ value of lamp to be tested at other end of bar. 

Let 100" = length of bar. 

Let X = distance from 1 to screen. 

Then 100 — x = distance from v to screen. 

The light-giving value varies inversely with the square of the 
distance; the more powerful light gives an equal illumination at 
a greater distance than does the weaker one. This gives the 
proportion and resulting equation: 

(100 — a?)^ 



1 : V :: (100 — a?) 
Let V = 2; then 



X- 

(100 — ic)^ S 



X-' 1 

• To obtain the place on the bar where this ratio holds, the 

2 
square root of both members of the expression -^ must be ex- 
tracted. This gives ^ Z as the ratio in which 100 inches must 

be divided. It may be done by proportion, thus: 

2.414 : 1.414 : : 100 : a; = 58.58 inches. 

Therefore, at points 58.58 inches from each end a 2 is to be 
marked on the bar. 

Next let V = 2, and we have ^ ^^ _ . 



PHOTOMETRY. 569 

The square root of 3 is 1.73; the ratio of parts of the bar isll??- 

which by the proportion 

2.73 : 1.73 : : 100 : x =: 63.37. 
gives 63.37 inches as points measured from right and left ends of 
the bar on which the figure 3 must be marlved. 

This is the simplest method as regards the arithmetic of the 
process by which the division can be effectually effected. As exe- 
cuted above, the decimals are not carried out as far as they should 
be. It is a case in which the work should be done by logarithms, 
not only for the sake of expedition, but to avoid errors in the 
operation. 

The Observation. — The candles — for in modern practice two are 
generally used simultaneously to give an average — are lighted 
and allowed to burn some five or ten minutes. They are placed 
on a balance and weights adjusted so as to make their end of the 
balance beam a few grains the heavier. As they burn they get 
lighter, and soon overbalance. The lamp to be tested is lighted 
and a voltmeter and ammeter are arranged for reading. The 
instant the candles overbalance, the time is taken and written 
down. The candles are carefully placed in position at their end 
of the bar, and the readings are taken every half minute until 
ten readings have been taken. At exactly five minutes from the time 
nqted, the candles are carefully blown out. If the ends stay red, 
they must be bent down with a pin until they absorb melted 
sperm, when they will at once expire. If the candles are not 
carefully blown out, grease will fly about, and the candles will 
lose weight. The candles are now weighed, and their percentage 
error is deducted or added to the average of the photometer read- 
ings. 

Suppose the candles burned 19.2 grains. This is an error of 
four per cent, for two candles in five minutes should burn 20 
grains of sperm. The candles gave too little light as they should 
have burned 10 grains in five minutes. Therefore four per cent 
has to be subtracted from the average reading. 

The candle balance is often mounted at the end of the bar, so 
that the candles are weighed there, and never need to be moved 
from their position. 



570 ELECTRICIANS' HANDY BOOK. 

Other Standards. — The French standard is the Carcel lamp, 
accurately defined as to its dimensions, and burning 42 grammes 
of colza oil per hour. Many precautions to be observed with the 
Carcel lamp have been formulated by MM. Dumas and Regnauit. 
The German standard is a paraffin candle burning with a flame 
of 50 millimeters (1.98 inches) height. The Munich standard 
is a stearin candle consuming 10.4 grammes of stearin per hour. 
The Violle standard, adopted by an international conference of 
electricians, is the light emitted by a square centimeter (0.39^ 
inch) of platinum at its temperature of solidification. It is not 
adapted for ordinary use, and it is questionable if it should ever 
have been adopted. The Heffner-Alteneck lamp is a simple round 
solid-wick lamp burning amyl acetate with a flame exactly 1.57 
inches high and regulated for each reading to that height. 
The French have another standard, the star candle, burning 154 
grains per hour. 

Table of Photometric Standards. — The following table gives 
the relative values of the more important standards of light: 



Violle 

Violle 1.000 

Carcel 0.481 

Star candles 0.062 

German candles . . . 0.061 

English candles . . . 0.054 

Heffner-Alteneck . . 0.053 

Shadow Photometer.— If a rod or bar is placed upright, and 
two lights are placed a few feet apart and a few feet back from 
it, they will cast two shadows upon an adjacent wall or white 
paper screen. The lights or one of them are moved back and 
forth until the shadows are of equal intensity; then the distance 
of each shadow from the lamp diagonally placed with reference 
to it must be measured. The illuminating power of the lamps 
will be in inverse proportion to their distance. 

Suppose a lamp which was being tested was 48 inches from 
the shadow appertaining to it, and the standard candle was 12 





Star German 


Engiish 


Heffner- 


Carcel 


candles candles 


candles Alteneck 


2.08 


16.1 


16.4 


18.5 


18.9 


1.00 


7.75 


7.89 


8.91 


9.08 


0.130 


1.00 


1.02 


1.15 


1.17 


0.127 


0.984 


1.00 


1.13 


1.15 


0.112 


0.870 


0.886 


1.00 


1.02 


0.114 


0.853 


0.869 


0.98 


1.00 



PHOTOMETRY. 



571 



inches from the other shadow. Then the illuminating powers of 
candle to lamp are as "48^ : 12% or as 16 : 1. 

In Fig. 440, E is the lamp under trial with voltmeter V and am- 
meter A, It is held on an arm carried by the spring clip H. C is 




Fig. 440.— Shadow Photometer. 

the standard candle on a scale G G. R is the rod whose shadows 

from lamp and candle are seen side by side on the paper screen S. 

This principle can be applied roughly in the street or elsewhere 




Fig. 441.— Bougtjer's Photometer. 

by comparing shadows thrown by two lamps, and pacing off or 
measuring the distances. A gas lamp can thus be compared with 
an arc lamp with some approach to accuracy. 
Bouguer's Photometer.— The cut, Fig. 441, shows another sim- 



572 ELECTRICIANS' HANDY BOOK. 

pie apparatus. The two lights under comparison ar3 placed on 
opposite sides of an opaque screen, and illuminate a translucent 
one of paper or ground glass placed at right angles to the sep- 
arating one. When both halves appear equally illuminated, the 
distances from lights to screen are measured, and the values are 
calculated by the law of inverse squares. The observer is sta- 
tioned on the further side of the translucent screen, 

Foucault*s Photometer. — This is a modification of the one 
just described. The opaque screen is moved back until the dark 
line or band at the junction of it with the translucent screen dis- 
appears. The cut. Fig. 442, shows the principle. In this way 

the comparison of the two divi- 
sions of the translucent screen is 
^ much facilitated. 

^,^' Direct Photometering: of an 

/'"" Arc Lamp is not very satisfactory, 

^" ^ ^ I on account of its richness in violet 

^"■^^ rays. The standard against which 

\^ • it is tried gives a light of a far 

\ different character. A very simple 

^. and practically efficacious instru- 

FiG. 443.— FoucAULT Photo- ment for testing the relative quali- 
METER. ties of arc lights is the luminom- 

eter. 
In this instrument the human eye in its every-day action of 
reading is made the measurer of the light. This is very logical, 
because the object of artificial light is to enable the eye to see, and 
the light may be measured by the ability of the eye to see things 
illuminated by the light examined. 

The Lurainometer.— It is a box. Figs. 443 and 444, containing 
a card of printed matter. Two tubes open into it. One receives 
the light from the lamp. The observer looks into the other, and 
sees the card illuminated by the light under trial. The light 
falls on it at such an angle that light is not reflected directly 
into the observer's eyes. The distance at which the card can be 
read is called the luminometer distance. The illuminating power 
is determined by this distance. The test gives the practical power 
of the light tested. 



PHOTOMETRY. 



573 



Two features characterize this instrument. One is its porta- 
bility. It can be taken anywhere and used in the open street. 
By using cards printed in various sizes of type, it can be ac- 
commodated to different distances. The other feature is its direct 
appeal to the eye. A light is produced to enable the human eye 
to see. This instrument tests the power of the light for this 
purpose. 

It is the invention of Mr. W. D'A. Ryan, of the General Electric 
Company. 

Pupillary Photometer.— The pupil of the human eye expands 




Figs. 443 and 444.— Lttminometer. 



and contracts virtually under the effect of varying intensity of 
light. The iris, in other words, acts like a diaphragm of a photo- 
graphic lens, and affords a larger or smaller opening according 
to the light acting on the retina of the eye. The pupillary photo- 
meter is based on this principle. It measures the diameter of the 
pupil of the eye when affected by different lights. This gives a 
coefficient of intensity of the light. 

Around the edge of a disk a number of pairs of holes are made 
near the outer ends of the radii. The holes of the different pairs 
vary in distance from each other. One pair of holes are sep- 



574 



ELECTRICIANS' HANDY BOOK. 



arated by a space of 0.07 inch. These are the closest spaced. 
The widest spaced are 0.38 inch apart. A second disk is pivoted 
over the first. It has a radial opening, which exposes one pair oi 
holes at a time. The light to be tested is looked at through a 
pair of holes. One pair after another is tried, until a pair is 
found whose edges seem to touch. There is a scale marked on 
the screen with a value for each pair of holes. It gives the 
diameter of the pupil which brings the two holes apparently in 
contact. The reading gives the relative brightness of the light, 
on the basis of the relative size of the pupil of the eye. The 
standard light is first looked at, and the holes which seem to 
touch are found for it. Then the light to be tested is examined, 
and the corresponding factor found for it also. 




Fig. 445.— Diffraction Photometer. 



Diffractive Photometer.— In testing powerful lights a concave 
lens is sometimes used to increase the diffraction of the rays and 
make it possible to use a shorter bar. The cut. Fig. 445, illus- 
trates the principle. The light given by the lamp E is diminished 
by the lens L in the inverse ratio of the squares of A and A'. 

Spherical Candle Power. — The electrician often takes a num- 
ber of photometric observations at different angles. To do this 
a standard or rated incandescent lamp is used as a standard. 
The value of this is known in candles when its voltage or am- 
perage are at a known value. The lamp to be tested is mounted 
so that it can be rotated horizontally or vertically. A number 
of observations are taken at angles numerous and diverse enough 
to represent the surface of a sphere, and the average of the 
observations gives the spherical candle-power. The lamp is 



PHOTOMETRY. 



575 



mounted on a support which can be rotated in all directions, 
and a number of observations at many angles are taken and 
averaged. The horizontal candle-power is averaged by rotating 
the lamp rapidly and photometering it while in motion. 

There are various methods of averaging the observations at 
different angles. A system ^ . 

employed at the Paris Expo- 
sition of 1881 consists in di- 
viding the surface of the im- 
aginary sphere into horizontal 
zones. The candle-power is 
determined for angles cor- 
responding to the center of 
each zone. These candle- 
powers are multiplied by the 
relative areas of the zones to 
which they respectively be- 
long. The sum of these 
products is divided by 4 ;r to 
get the mean spherical 
candle-power. The factor 4 7t 
is taken as the area of a 
standard sphere. 

The cut. Fig. 446, shows 
an apparatus for taking 
spherical candle-power of an 
incandescent lamp. The 
lamp is mounted so as to be 
rotated rapidly by an electric 
motor. This gives an aver- 
age illumination all around, 

and the candle power is determined while it rotates. It is 
mounted so that it can be inclined at various angles from the 
vertical while still rotating. Observations of candle-power 
are taken while it is in various positions, as indicated on the 
scale D. An average of the observations is taken as giving the 
candle-power. 

If the candle-power is determined at different angles in the 




Fig. 



446.— Apparatus for Spherical 
CandijE-Power. 



576 ELECTRICIANS' HANDY BOOK. 

horizontal plane, it is generally enough to determine one set of 
vertical-angle candle-powersi — the candle-powers at various angles 
on one meridian. The corresponding candle-powers on the re- 
maining meridians may be calculated from the relations of the 
different candle-powers on the horizontal plane. If the lamp is 
rotated as described, the average is given directly as far as the 
different horizontal angles are concerned. 

Candle=Powers of Incandescent Lamps.— The horizontal candle- 
power of an incandescent lamp is its maximum, but the ratio of 
horizontal to spherical varies greatly according to the shape of the 
filament. The table gives the mean spherical and mean horizontal 
Intensity of several incandescent lamps. 

Mean Spherical Mean Horizontal 

Candle-Power. Candle-Power. 

Edison 15.49 18.83 

Stanley 13.56 16.54 

Woodhouse and Rawson. . . 15.09 19.11 

White 12.44 15.08 

Weston 16.27 17.87 

The candle-power at different vertical angles varies very greatly. 
The tip on the top of the bulb diffracts light, and reduces the 
vertical candle-power at that end, while the base of the lamp 
reduces it to zero at the other end. It will be sufficient to give 
a set of candle-powers for an Edison lamp taken at vertical angles 
of 0°, 30°, 60°, and 90° all around the lamp. 0° gives the hori- 
zontal plane, 

0°, 16.70; 30°, 15.02; 60°, 9,54; 90°, 3.57; 120°, 8.25; 

150°, 14.96; 180°, 16.82; 210°, 14.84; 240°, 9.07; 270°, 0.00; 

300°, 9.84; 330°, 15.06, 

The Photometry of the Arc Lamp is far from satisfactory. 
The carbons are never perfectly homogeneous, are almost certain 
to be a little out of center, and this causes the horizontal candle- 
powers to vary greatly. After burning a little while, carbons are 
apt to bend a little, which throws the ends out of line with each 
other. The candle-power in one direction on the horizontal plane 
may be twice or three times as great as in the other. The maxi- 
mum candle-power is found many degrees removed from the 



PHOTOMETRY. 577 

horizontal. This varies far less at different meridians than does 
the horizontal candle-power. 

The variations at vertical angles are very great. A direct- 
current arc gave the following candle-powers at different vertical 
angles: 

Above the horizontal, 60°, 48; 30°, 110. 

At the horizontal, 0°, 208. 

Below the horizontal, 10°, 401; 20°, 612; 30°, 871; 40°, 1,000; 50°, 
807; 60°, 457; 70°,, 188. 

As arc lamps are used, the mean spherical candle power is of 
little importance, and it is not often determined. It is a laborious 
operation, as the great irregularity of the distribution of light 
requires a large number of observations at small angular distances 
from each other. A short road to the result is that proposed at 
the Paris Electrical Exposition of 1881. The average horizontal 
candle-power is divided by 2 and added to the maximum candle- 
power divided by 4. The sum is taken as the spherical candle- 
power. 

Thus a Brush arc lamp gave a mean horizontal candle-power of 
909 candle-power; a maximum candle-power of 4651 candles; 
and a spherical candle-power as calculated, 1776 candles; and 
spherical candle-power by observation, 1675 candles. 

The formula reads thus: 

^ H M 

S-Y + T 

in which S is the spherical candle-power, H is the average hori- 
zontal candle-power, and M is the maximum candle-power. From 
a number of observations it is found that the formula gives an 
error of 1 to 14 per cent. 

Mechanical Equivalent of Liglit. — Light is the action of cer- 
tain ether waves upon the retina of the eye. If light is decom- 
posed by means of the prism, the visible spectrum will be em- 
braced within relatively narrow limits. The violet end of the 
spectrum has its color produced by the shortest waves that affect 
the eye. A musician would say that violet was a very high note, 
or at the top of the scale. Beyond the violet there are waves 
which are so short that the eye does not take cognizance of them. 
These rays act with great energy on chemical agents such as salts 



578 ELECTRICIANS' HANDY BOOK. 

of silver. A photograph can be taken by means of them. If 
separated from the other rays, they would enable a photograph 
to be taken in a dark room. 

Going to the other end of the spectrum, the red appears due 
to relatively long waves or high heating power. Below the red 
is a long stretch of spectrum quite invisible, but producing heat. 
By a sensitive thermometric apparatus the spectrum can be fol- 
lowed out a long distance below the scale of visibility. 

A micron is about one twenty-five-millionth of an inch or one 
one-millionth of a millimeter. The shortest wave length of vis- 
ible light is 0.360 micron for normal eyes. Dark red light has a 
wave length of 0.810 micron, and 1.000 micron is the utmost range 
of visible light. This is a range of 0.640 micron, within which all 
visible rays must lie. Above this range is the ray of invisible 
actinic radiation, "invisible light" it is sometimes paradoxically 
called, due to the spectrum of radiations less than 0.185 micron 
long. Below the spectrum we have heat radiations, due to waves 
less than 30 microns long. Thus without fncluding Hertz waves 
it appears that in a range of nearly 30 microns only 0.640 micron 
is visible, or in decimals 0.021 of the entire scale of naturally-pro- 
duced ether waves. 

Light being a physiological effect of a natural cause can hardly 
be said to possess a mechanical equivalent. Yet if we determined 
the mechanical equivalent of the entire radiations of a given 
spectrum, and subtracted therefrom the proportion which was ob- 
scure, we would obtain a figure that might be taken as the me- 
chanical equivalent of light. This has been done. The total 
energy of the rays from a source of light was determined by an 
air thermometer. The air expanded under the influence of the 
total heat received. The luminous rays were screened out by a 
dark solution, such as one of iodine, and the heat imparted by 
the invisible rays was determined. A thermo-electric pile was 
employed for this. The experiment by Tumlirz is described in 
"Wiedemann's Annalen. 

He found that the light given by the Heffner-Alteneck lamp, 
which is 0.98 standard candle, was 0.00361 gramme degree C. 
calorie per second, or 151,500 ergs per second. This corresponds 
to the energy rate of a current of 0.1226 ampere through a re- 



PHOTOMETRY. 579 

sistance of 1 ohm. By Ohm's law E = RI. This gives a voltage 
of 0.1226 volt. The electric energy is 0.1226 X 0.1226 == 0.0150 
volt-ampere, or watt. 

The pupil of the eye covers a very small portion of the spherical 
area of illumination. If the eye were 1 meter (39.37 inches) from 
the light, and if its pupil were 3 millimeters (0.118 inch) diam- 
eter, the light it would receive on the above basis would require 
a year and 89 days to raise 1 gramme (15.403 grains) of water 
1° C. or 1.8° F. 

If the physiological aspect of the subject is dropped, the above 
may be taken as of value. It gives with reasonable closeness the 
mechanical equivalent of rays which afEect the human eye. 

The mechanical energy expended by a source of light may be 
divided by the units of light which it gives. The quotient is a 
practical figure expressing the relative economy of the source 
of light, and this figure is sometimes incorrectly called the mech- 
anical equivalent of light. 

Thus a 16-candle-power kerosene lamp was found to burn 
oil enough to represent 37 calories per hour per candle. This 
gives 428.6 meg-ergs per second, a rate of energy equal to 42.8 
watts. A gas burner required 68.8 watts per candle-power. An 
incandescent lamp is generally allowed 3.5 watts per candle-power. 
The arc lamp may go as low as 0.8 watt. 

The light of the spectrum is due to ether waves succeeding 
each othei' approximately between 4 X 10" and 7 X 10" times per 
second. In a second they travel about 180,000 miles. If we divide 
this by the number of waves per second of any given light, 
we shall obtain as quotient the length of such wave. As, roughly 
speaking, light travels a little over 10^^ inches per second, the quo- 
tient of 10^ ^ 10^* would be one 1/1000 of an inch. On the basis 
of 4 X 10" waves per second, such wave would be about 1/4000 
inch long. 

Watts per Candle=Power in Arc Light.— The watts per candle- 
power for direct-current arc lamps vary from 0.60 to 1.13 watts; 
for alternating-current arc lamps, from 1.13 to 1.80 watts. As an 
interesting example of the practice of some years ago, the Jabloch- 
koff candle may be cited. At 200 candles it used 2.80 watts per 
candle, and at 500 candles 1.81 watts per candle. 



580 ELECTRICIANS' HANDY BOOK. 

Watts per CandIe=Power in Incandescent Lamp.— In incan- 
descent lamps at high efficiency 2.5 watts may be absorbed per 
candle-power. Lamps run at this efficiency soon break down. A 
low efficiency is 3.5 watts, when the light given is expensive with 
regard to the power absorbed. The mean figure of 3 watts to the 
candle-power represents good average practice. 

Quality of Arc Light. — The diagram, Fig. 447, taken from 
Abney, shows the proportions of the different rays of the spectrum 
in gas, arc, and sunlight. The curve of gaslight may be taken 
as practically that of the incandescent carbon-film electric lamp. 
To obtain a light pleasing to the eye, too much of the light of the 



/^^^^''^^ 




/^. \'" 




r \ \ 




//' Gas-\ \\ 




y^' "^^-S^ 




..^i!r\ 1 1 "~H^^:=?^=:== 





BCD E F G H 

Red Violet 

Fig. 447.— Qualities of Diffebent Lights. 

violet end of the spectrum should not be present. The sun may 
be taken as giving the mixture which it should be the object of 
the engineer to imitate in producing artificial light. The arc's 
light, it will be seen, approaches closely to the composition of 
the light of the sun. 

A convenient way to remember the succession of colors in the 
spectrum is by the combination vibgyor, indicating violet, indigo, 
blue, green, yellow, orange, red. Lithium chloride gives a bril- 
liant red light when a wire dipped into it is held in an alco- 
hol or Bunsen-burner flame. Copper gives a green, salt a yellow 
light. The rays of short wave length, such as violet, are not 
easily produced except when accompanied by other rays. The 
mixture of light of all colors gives white light. This is what is 
needed by mankind for illumination. 



PHOTOMETRY. 581 

In photometering arc lamps, as we have seen, values widely 
differing are found at different vertical angles. These values for a 
given lamp, with specific carbons, current, and other factors, are 
reasonably constant. The horizontal angle should make no differ- 
ence if the lamp works perfectly. But invariably the departure 
from centering of the arc shifts the hottest point of the carbon 
to one side, so that in practice a difference may always be antici- 
pated. 

Arc lamps have received a sort of trade valuation — that of 
2,000 candles. This has long been recognized as grossly inaccu- 
rate and in excess of the truth. The so-called 2,000-candle-power 
lamp is one of standard size using less than 500 watts. The 
present standard is 10 amperes and 48 volts, or 480 watts. From 
such a lamp by manipulation at the photometer 1,700 or 1,800 
candle-po\ver can be obtained as a maximum. The average maxi- 
mum candle-power for a direct-current lamp at a vertical angle 
of 45° is about 1,250 candles. 

The alternating-current lamp distributes its light symmetric- 
ally above and below the horizontal plane. The direct-current 
lamp distributes its light principally below the horizontal plane. 
There is a distinction between open-arc and inclosed-arc practice. 
The open-arc lamp works with its carbons much closer together 
than does the inclosed arc. As we have seen, about 85 per cent 
of the light comes from the crater in the positive carbons in direct- 
current lamps. In alternating current, 95 per cent comes from 
the carbons. The adjustment of the carbons, if varied by the 
smallest amount, changes the distribution of the light. The arc 
is about one-eighth inch long. A small fraction of an inch makes 
a considerable difference in so short a distance. 

The inclosed arc is produced between carbons which are consid- 
erably farther apart. The slight changes in feed are referable 
to a longer distance, and hence affect the arc less in proportion 
than for the shorter-distanced carbons in the open-arc lamp. The 
carbons in the inclosed arc burn with flat ends. The arc travels 
about between the disk-shaped ends of the carbons. The arc in 
open-arc lamps also shifts about, but its movements affect the 
distribution of the light much more. Figs. 448 and 449 show 
results from photometry of open-arc and inclosed-arc lamps. 



582 



ELECTRICIANS' HANDY BOOK. 



The distances from center of carbon space to the curves give the 
relative values of the candle-power at different vertical angles, 
of the candle-power at different vertical angles. 

The long arc diminishes the screening effect of the lower carbon. 
If carbons are fed close to each other, the lower one will cut ofE 
part of the light which would otherwise reach the ground. 




Fig. 448.— Distribtjtion or Light from an Arc Lamp on Pole. 



Distribution of Light from Arc Lamps in Service.— The illus- 
trations, Figs. 448 and 449, show the distribution of light in the 
vertical plane from arc lamps. The curve A in both diagrams 
gives the distribution of light from an open-arc lamp using 9.6 
amperes of direct current. Of high illuminating power near the 
lamp, it rapidly drops off. The curve B is that corresponding to 
the light from an inclosed-arc lamp using 6.6 amperes of direct 



PHOTOMETRY. 



583 



current also. The distribution of light is far evener than in the 
case first cited. The curve C corresponds to the light from an 
inclosed-arc lamp using 7.5 amperes of alternating current. The 
diagrams are so fully marked as 
to be virtually self-explanatory. 
We are indebted for them to 
the General Electric Company. 

Distribution of Light from 
Incandescent Lamps.— The light 
given by incandescent lamps in 
different directions varies great- 
ly. The single-loop filament 
gives the most irregular distri- 
bution, varying from an average 
for the horizontal plane of 16 
candles down to 5.7 candles 
from the tip. The small quan- 
tity of light given from the tip 
is due largely to the glass tip 
or point refracting the light in 
all directions, which falls upon 
it, A lamp whose filament has 
two turns in it gives a much 
evener distribution from 16 
candles down to 10 candles. 

It is not of great importance to have even distribution of light, 
because the lamp can be adjusted to give the most favorable as- 
pect to the reader or user of it, and because incandescent lamps 
are so often put in clusters, which tends to even matters. 




Fig. 449.— Distribution of Light 
FROM AN Arc Lamp. 



CHAPTER XXXIV. 

THE ELECTRIC RAILWAY. 

The Electric-Car flotor is constructed with a view to pro- 
tection from mud and water. It is accordingly inclosed in an 
iron case, and this case is used as part of the field magnet. From 
its interior the poles project inward, and field coils are placed on 
these poles. A drum armature revolves inside the case. On the 
end of the armature shaft a pinion is mounted. This gears into 
a large gear wheel on the driving axle of the car. 

Such is the general outline of the trolley-car motor as now 
constructed. 

Standard Voltage and Allowable Temperature. — The trolley 
systems have a standard voltage of 500 volts. The motor capacity 
is rated as horse-power, which refers to the power it can develop 
without getting overheated. The temperature of 167° F. (93° C) 
is considered a sort of standard allowable rise of temperature. 
Motors are often rated on the power which can be developed 
continuously for an hour with a rise of temperature of 167° F. 
(93° C). This rise is generally based on an atmospheric temper- 
ature of 45° F. (7' C.) as a starting point, thus giving the tem- 
perature of boiling water as the allowable temperature of a mo- 
tor. 

In practice the motor is cooled to a considerable extent by 
the motion through the air. It is thought that this is good for 
about 20° F. (11° C.) reduction from the above figures. 

Cause of Motor Heating. — The heating of a motor indicates 
core loss and copper loss. The first-named source is caused 
by eddy currents, and varies principally with the voltage. 

The Copper Loss is the heating of the wires by the current 
passing through them. The heating effect of a current varies 
with the energy rate or with the volt-amperes, or watts. 

584 



THE ELECTRIC RAILWAY. 585 

We have as the formula for watts I E, and by Ohm's law 
E = RI 
and substituting for E this value we have 
Watts = I E = R I^ 

This states that with constant resistance the watts absorbed 
by a conductor vary with the square of the current, and therefore 
the heat developed varies with the same. 

The copper loss is determined from the current intensity and 
varies with the square of the current, and for a continuous current 
the practical determination is easily made by running the motor 
and ascertaining its heating under different loads. A thermom- 
eter gives the temperature. This is very simple; but when vary- 
ing currents are in question, the difficulty of reaching a conclu- 
sion as to the permissible average current is considerable. The 
heating effect varying with the square of the current, a mo- 
mentary increase of current produces far more than its direct 
proportion of heat. Suppose the current doubled for a few 
seconds. During that period it is developing four times the 
heat it did at the lower rate. 

The heat developed by an irregular current varies with the 
mean square of the current. The greatest allowable average cur- 
rent is equal to the square root of the mean square of the current. 
It is estimated that this quantity for ordinary street-car service 
will be about 35 per cent greater than the average current. 

Thus, if a motor could without overheating pass a steady cur- 
rent of 50 amperes, it could pass approximately an average cur- 
rent of 38 amperes under the conditions obtaining fn street-car 
service as assumed under the above estimate. 

This would be a most valuable figure, were it not that it ap- 
plies only to an estimated condition of a particular service. Ac- 
curacy can only be reached by a determination of the average 
current for each specific case. To determine average current, 
the ammeter should be put in series with a single motor, where 
the series-parallel system is used. Where this system is in use, 
the current per motor is generally a good deal in excess of half 
the total current. The reason is that when the motors are put in 
series, each one takes the total current. 

Determining the Heating of Motors.— This may be done 



586 ELECTRICIANS' HANDY BOOK. 

roughly by the use of thermometers on the outside of the coils. 
Another more satisfactory way is by determination of resistance 
before and after a run. The resistance of copper varies as the 
temperature varies, and from a table of resistance changes due 
to temperature changes, the heat to which the conductors are 
subjected can be calculated. 

Conditions Causing Heating. — An insulating material which 
is an especially poor conductor of heat and lack of ventilation of 
the armature cause high temperature in motor windings. 

Horse=Power of Car flotors, — A fair allowance of tractive 
power for average conditions is about 20 pounds per ton 
weight on a level, with an addition of 20 pounds for each per 
cent increase of grade. "Within reasonable limits of speed these 
figures do not change greatly. A spring balance placed as a 
coupling between a motor car and a trailer would indicate on 
level ground a pull of about 200 pounds if the trailer weighed 10 
tons. Horse-power varies with the product of force by space tra- 
versed per second. The horsepower with approximately con- 
stant tractive effort would vary approximately with the speed. 
If the speed of a moving car and its traction in pounds are. 
known, the horse-power can be calculated. 

A horse-power is 550 feet per second multiplied by one pound, 

which is 1,980,000 feet per hour multiplied by one pound. 

(1,980,000 = 550 X 3,600; 3,600 = the seconds in one hour.) This 

can be put thus for a car in motion: 

Feet per hour X Traction in pounds 

Horse-power = . 

1,980,000 

There are 5,280 feet in one mile, therefore 

Feet per hour =: miles per hour X 5,280. 
Substituting this value in the last formula, we have: 

Miles per hour X 5,280 X Traction in Pounds 



Horse-power =: 



1,980,000 
Dividing both numbers by 5,280, we have: 

Miles per hour X Traction in pounds 



Horse-power ==: 



375 

Suppose a 20-ton car is going up a 2 per cent grade at 16 miles 
^n hour. The traction on the level grade at 20 pounds to the ton 



THE ELECTRIC RAILWAY, 



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588 ELECTRICIANS' HANDY BOOK. 

would be 400 pounds. Allowing 20 pounds more traction per ton 

per each per cent of grade, the traction on a 2 per cent grade 

would be 1,200 pounds. The formula is now applicable. 

16 miles per hour X 1,200 pounds traction 

Horse-power := — 

o75 

giving 51.2 horse-power. 

Traction Table. — The table. Fig. 450, gives traction data. The 
central column of figures gives the tractive effort. Car weights 
are given at the bottom on the left. The vertical line rising from 
any given car weight intersects the lines of grades. If from 
any such intersection the horizontal line is followed to the right, 
it will give the tractive effort to move a car of that weight up 
the grade in question. Thus, a 20-ton car on a 10 per cent grade 
will require a little over 4,300 pounds traction, or drawbar pull 
if it were a case of towing. 

On the right hand is given horse-power at given traction and 
speed. Thus, taking any given traction and following out the 
horizontal line, it intersects different speed lines. If from any 
intersection the vertical line is followed down to the base, it 
will give the horse-power. Taking 4,300 pounds traction of the 
last example at 10 miles an hour, the vertical line from its inter- 
section with the 10-mile-an-hour line leads to about 115 horse- 
power. 

Construction of Electric=Car flotor. — The general features of 
a standard railway motor may be thus summarized: 

There are four field poles projecting radially inward from the 
iron case, which constitutes in itself a portion of the field mag- 
nets corresponding to the yokes. The yoke or case is of steel 
casting; the projecting poles are of laminated iron or disks. These 
are fastened together, and are cast into the yoke. The yoke is 
made in halves, hinged at the side parallel to the car axle, so that 
the case can be opened like a box. The field is shown in Fig. 
451, opened with the poles projecting as described. 

The field coils are wound upon molds in a lathe, and are in- 
sulated with mica and fuller board. Each coil is solidly made, 
und slips over a pole piece. Cast brass pieces bolted to the yoke 
Aold each coil in place. Two field coils are on poles in the upper 
half of the case. Their terminals are soldered to insulated wire 



THE ELECTRIC RAILWAY. 



589 



pieces several feet long, to keep them out of the way of the 
brush holders. The coils in the lower half of the case have me- 
tallic terminals. 

A slotted drum armature of disk or laminated structure is used. 
Holes are made through the assemblage of disks to secure ventila- 
tion, in order to keep down the temperature. A low temperature 
conduces not only to higher power capacity, but to efficiency and 
to security from injury. The winding of the coils is designed 
to secure ventilation. Three coils are wound together and are in- 
sulated in a casing, which is then placed in the slot in the arma- 
ture. No bending or hammering into place is needed or used. 




Fig. 451.— Cab Motor Field Opened. 



Steel binding wires, themselves sunk into grooves running around 
the armature at right angles to the conductor grooves, hold the 
armature coils in place. The imbedding of these wires prevents 
them from cutting if the armature should become so badly dia- 
placed as to strike the field poles. 

The commutator is of the regular mica-insulated type. The 
brush holders are fastened to the upper half of the case. 

The armature shaft carries a forged steel pinion. This works 
into a cast-steel gear wheel on the driving axle of the car. Stand- 
ard gear ratios are 58 to 24, 64 to 18, and 68 to 14. Th-^se are 



590 



ELECTRICIANS' HANDY BOOK. 



such that the teeth will constantly change in relation, the same 
teeth coming together but seldom as the gears rotate. 

A large air gap is allowed between field poles and armature. 
This, although disadvantageous from the point of view of the 
permeance of the magnetic circuit, minimizes the effects if the 
armature should get out of center. One of such effects is a strong 
side pull exerted by the nearest pole or poles. If the air gap is 




Fig. 453.— Cab Motor Opened. 



large, a given displacement, a tenth of an inch for instance, is 
much less proportionately than it would be with a small air gap. 
If the air gap were one-tenth of an inch, such displacement might 
be termed 100 per cent; if the air gap were half an inch, it would 
be only 20 per cent on the same basis. 

A typical car motor with the field opened is shown in Fig. 452. 

Switch Boxes and Circuit Breaker.— The current from the 
trolley pole connection goes first to a switch placed over the plat- 



THE ELECTRIC RAILWAY. 591 

form on the under side of the projecting roof or canopy. There is 
another of these switches at the other end of the car, and the 
two are in series with each other. The current enters by one 
switch, goes through it, and a conducting wire leads to the other 
switch, and from it the current is led to a fuse hox or mechanical 
circuit breaker. The two switches are called canopy switches, 
main motor switches, auxiliary or overhead switches. There is 
generally an electro-magnet in the switch box, which prevents 
any arc from forming when the switch is opened. The magnet 
repels the arc, and puts it out as a draft of air puts out a candle, 
although on widely different principles. It is called a blow-out 
magnet or magnet coil. 

Lightning Arresters. — After passing the circuit breaker, or else 
the fuse box if such is used, the lightning arrester is reached. 

The old lightning arrester consisted of two plates with saw 
teeth secured so that tooth faced tooth at a small distance. The 
circuit to be protected has one of its leads attached to one of the 
plates, and thence goes on its regular course. The other plate is 
grounded. If lightning enters the system, it easily breaks across 
the air gap and goes to earth before it reaches the controller, dy- 
namo or other appliances. Lightning has such high potential 
that ohmic resistance means little to it. But it is of oscillatory 
character, and a relatively slight inductance will resist its passage 
strongly. In the course of the circuit as it leaves the lightning 
arrester a choke coil is placed. This is of slight ohmic resistance, 
and has a negligible effect on the working current of the system. 
When lightning enters the circuit, this acts by its inductance to 
hold it back and to force it to the earth over the gap in the light- 
ning arrester. 

Another lightning arrester has two carbon terminals with 
their ends close together but not touching. The lightning gap 
is at this point. If lightning strikes the circuit, it springs across 
the gap and goes to the earth. A coil of wire surrounds the upper 
end of one of the carbons and extends some distance above it. 
Within the coil is an armature lying loosely in it. If the arma- 
ture is raised, the circuit is broken. If the main current follows 
the course of the lightning, it excites the coil, and the armature 
springs up. This breaks the circuit, and the arc is destroyed, and 



592 ELECTRICIAN l^' HANDY BOOK. 

the armature dropping back to its place, the current goes on its 
regular course. Other lightning arresters are described elsewhere. 

Controllers. — The speed of rotation of a street-car motor and 
coincidently the speed of the car is regulated by giving it more 
or less power. The volts of potential difference which produce 
a current through the car connections and wiring are constant as 
near as may be. There are in modern practice always two or four 
motors in a car. For low power the voltage which acts upon, 
each motor or pair of motors is reduced to less than half that of 
the circuit. For high power each motor or pair of motors is 
given the entire voltage of the circuit. 

There are several controllers in use, the Westinghouse and the 
General Electric Company's being very extensively employed. 
The general principle is the following: 

A vertical shaft is mounted in a case, generally placed against 
the dashboard of the car. The case is of sheet iron, approximately 
semi-cylindrical in shape, with a door which opens its entire 
height. The shaft is square on top, and a crank handle fits on the 
square end. Upon the shaft are mounted a number of horizontal 
cams. In a typical controller there are eleven. They are insu- 
lated from the shaft, and are connected together in groups or 
pairs. The shaft is never turned through a full circle. The cams 
are of such shape that their working or contact faces are arcs 
of circles, concentric with the center of the shaft. Some of the 
arcs are so long that their angular scope is equal to the extreme 
range of motion of the shaft. Thus, if the shaft moves through 
200°, the largest cams would include 200° in their arc. Other 
cams are very short. They are distributed as regards their work- 
ing surfaces or contact arcs over the whole range of the angular 
movement of the shaft. They are secured to the shaft at even 
distances apart vertically. 

By the side of the cam shaft is a series of contact fingers. 
These are exactly similar one to the other, and arranged vertical- 
ly and spaced so that there is one finger for each cam. If the 
shaft is turned to the extreme right, no finger will touch a cam. 
If turned to the left, the fingers will make contacts. The order 
of the contacts and the duration of each one depends upon the 
arrangement of the cams and on their extent of contact surface 



THE ELECTRIC RAILWAY. 



593 



or arc. If the cam surface is long enough, the finger will, once 
it is brought in contact with it, remain in contact for the full 
swing of the handle. If the cam surface is short, its finger may- 
come in contact with it for a short period and then leave it. The 
construction of a controller is shown in Fig. 453. 

Controller Points.— On the plate which covers the top of the 
controller case are cast a series of short radial bars or "points," 
distributed on the arc of 
a circle concentric with 
the shaft and cams. Each 
point indicates a position 
of the handle. A hori- 
zontal wheel is fastened 
to the shaft immediately 
below the cover. This 
has rounded notches in 
its edge, one for each of 
the points. A sort of pawl 
drops into these notches 
as the wheel is rotated by 
the handle. The notch 
and pawl fix the shaft in 
place, and also disclose to 
the motorman that a point 
is reached. If he counts 
the notches, he will know 
where his handle is with- 
out looking at the points. 
A qualified motorman need 

never take his eyes off the road in front. If in doubt as to what 
point the handle is on, he can turn his handle clear back to the 
starting point and then return it, counting the notches one by 
one as he passes them until the desired one is reached. It is not 
a matter of indifference which points are used; there are pre- 
ferred driving points which should always be used. 

Driving Points. — Some points indicate a maximum of resist- 
ance in series with the motors. Other points indicate less re- 
sistance in series, and there are two or three points which indi- 




FiG. 453.— Trolley Cab Controller, 



594 ELECTRICIANS' HANDY BOOK. 

cate no resistance in series. The general law for the con- 
centration of resistance in machines absorbing energy applies 
here. The points indicating no resistance are the ones on which 
the car should be driven. The energy is not wasted in external 
resistance as it is on the other points. The driving points are 
cast longer than the others, so as to be clearly indicated to the 
motorman. 

Series = Parallel Controller. — A large variety of controllers 
of this type are made, adapted for different-sized cars and mo- 
tors. Naturally, a high-powered car needs more regulating con- 
tacts than does a low-powered one. 

The term series-parallel indicates that the two motors on a car 
are operated sometimes in series and sometimes in parallel. 
This gives two speeds. Intermediate speeds are produced by a 
set of changes, each one involving a definite step. There is no 
gradual transition, but a step-by-step progress from low to high 



A nine-point controller controls by the following combina- 
tions: 

When the handle is turned to the first point, it brings into a 
series of three a resistance and the two motors, one behind the 
other. The current flows through the resistance, which cuts it 
down wastefully. Then it goes through one motor, and it is still 
further cut down, but here not wastefully, and then goes through 
the other motor, and then to the ground. This connection gives 
the least energy to the motors that is possible as the connections 
are arranged. 

On moving the handle to the second point, a portion of the 
resistance is cut out; on moving it to the third point, fourth 
point, and fifth point, resistance is cut out each time, the motors 
remaining in series. As the system is run on constant potential, 
the movements described have increased the current given to the 
motors, and therefore have increased the power developed by 
them, and^ the car under equal conditions increases its speed. 

At the fifth point all the resistance is cut out, and the motors 
are left in series. This is the first running point, as there is 
no wasteful resistance in series with the motors. The rule thai 
resistance should be concentrated in the motor applies here. 



THE ELECTRIC RAILWAY. 



595 



The handle now swings through a transition stage in which 
(a) the motors again have resistance in series with them; (&) 
one is cut out, the other having the same resistance in series with 
it; c the same as &; and the sixth notch is reached. There are 
no notches for positions «, &, and c; the handle swings by them 
to the sixth notch, at which most of the resistance is in series, 
and the two motors are in parallel. This gives more power. 
The seventh notch cuts out more resistance, the eighth still 
more, and at the ninth notch cuts out all the resistance and the 



1 -2 3 4 5 6 7 8 9 10 T1 12 




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Fig. 453a.— Development on CoNTROLiiEB Connecttons. 



motors are left in parallel, with the full potential and maximum 
current acting on them. 

The cut, Fig. 453a, shows the development of this controller. 
The cam faces are supposed to be straightened, and the successive 
points and the connections for each are indicated. The fingers 
only make contacts when over the cams. Thus at point 3 and at 
all subsequent points finger No. 2 is cut off. It only makes con- 
tact at points 1 and 2. The cam faces are connected with each 
other, as indicated by the lines. If the description is followed 
with constant reference to the cut, the operation will be clear. 

There are other arrangements of controller. In some the con- 
troller throws a shunt in parallel with the motor fields, thus in- 



596 ELECTRICIANS' HANDY BOOK. 

creasing the speed, the armature taking a still greater current. 
For high-power motors more points may be given, sometimes as 
many as thirteen, with the seventh and thirteenth as running 
points. 

Hot Resistance. — If a car is run upon the wrong point the 
resistance is heated, and a hot resistance indicates wasteful 
running. A car should be run on the driving points as much as 
possible, except when it is allowed to coast or drift with all 
power off. 

Blow-Out Magnet.— In the controller case is an electro-magnet 
whose function is to blow out arcs. As the fingers slip from cam 
to cam, there is constant danger that arcs will form. The electro- 
magnet has hinged to one pole a plate of metal, which shuts 
over the cam shaft and contact fingers like a door, and forms a 
prolongation or extension of one of its poles. On the inside 
face are secured a number of blocks of insulating material, cor- 
responding to the spaces between the successive cams. These 
go into the gaps, and separate each cam with its finger from its 
neighbor. In the cut. Pig. 453, already referred to, the hinged 
pole piece is shown swung back, and the asbestos composition 
insulators are shown projecting from it. The magnetic field 
extinguishes arcs as fast as they form. 

Reverser, — To the right of the cam shaft is a reverser. This 
operates by reversing the relations of the field and armature con- 
nections. 

Board and Cut=Outs. — In the bottom of the case is a board, 
to which the wires from the motors and resistances are con- 
nected, as directed in the wiring plan, which the electric manu- 
facturing company supplies. Two knife cut-out switches are here. 
They have wooden handles, and are numbered 1 and 2. Each one 
cuts out or in its own motor, according to the number inscribed 
upon it. 

Rheostat Controller. — In this system the changes in current 
are brought about by changing the resistance in series with 
the motor or motors. Some resistance is always in series, ab- 
sorbing energy, except when the car is running at full speed in 
the rheostat system. This involves waste of energy. The sys- 
tem is out of date. 



THE ELECTRIC RAILWAY. 597 

Motorman*s Duties. — Various directions are given for running 
trolley cars. Several books are published devoted to the motor- 
man's work. Generally, more than one car is operated on a line, 
and it is fair to say that on all small roads where much business is 
done a broken-down car will be pushed to the car stable by the 
next car. General directions for making repairs can be given, 
but cars differ from one another in their electrical equipment. 
An electrician in charge of the repairs of cars of a road will have 
to study their special machinery, and especially the connections 
used in the cars whose repairs come under his charge. The 
motorman will only be expected to make the simpler kind of re- 
pairs, and may be forbidden to do even that much. Outside of 
this function, the motorman has very specific duties to perform 
in running his car properly. It is stated by one author that by 
actual trial he found one competent motorman ran his car with 
one-half the power which an incompetent one required. 

Economical Running.— It is wasteful of energy to turn power 
on suddenly. A jerk involves waste of energy, and shakes the 
whole structure of the car. The power can often be shut ofC on 
slight down grades. When the track is obstructed, instead of 
running up to the obstacle under power and then putting on 
the brake, the power may be shut off a considerable distance be- 
fore the obstacle is reached, and a comparatively slight applica- 
tion of the brakes will suffice to stop or slacken the speed of the 
car as required. 

Excessive Use of the Brake is hard on the brake shoes and 
wheels. If the wheels are completely arrested, so that they slide 
on the track, it is apt to wear flat places on them. They then 
need grinding or turning to restore their circular contour. If a 
wagon is on the track, the car can be slowed by turning off the 
pov/er while it is still a good distance away, and the wagon may 
turn out while the car is still coasting. Waste of energy would 
result from running up to the wagon under power and suddenly 
turning off the power and putting on the brake at the last minute. 

Bad running exhausts the motorman also. The excessive use 
of the brake is hard work fn the fullest sense of the term. 

Flat Wheels, — This term is applied to wheels which have had 
flat places worn upon them. They make a most disagreeable noiso 



598 ELECTRICIANS' HANDY BOOK. 

when the car is running, and expense is involved in grinding or 
turning them to shape. 

Sliding Wheels. — Wheels caused to slide by excessive braking 
do not stop a car as quickly as wheels which turn so as to con- 
stantly present a new surface to the rail. If held so that they 
cannot turn, the spot in contact wears smooth and slides along 
with less friction than in the other case. 

Skidding Wheels. — If wheels turn without moving the car, use 
a little sand. Turn the power off, and then slowly on again to the 
last notch. 

If wheels slide on slippery rails, when the brakes are put on, 
do not apply sand. First throw off the brake, start the sand, and 
then apply the brakes again. 

Reversing.— Never reverse the car until the controller handle is 
in the off position. The car should first be brought to a stop, the 
reversing lever turned, and then power should be slowly given. 
The trolley pole should always be shifted, except for very short 
distances. 

Leaving the Car, — If the motorman leaves the car, he should 
turn the controller completely off and take the handle with him, 
otherwise some unauthorized person may interfere, and turn on 
the power. 

Bad Ground. — If the rails are dusty, the car may refuse to start 
because it makes a very poor ground. Rocking the car by sway- 
ing and almost jumping on the platform may give a ground to 
a motionless car which has refused to start. The rail may be 
cleaned of dust a short distance from one of the wheels, and a 
ground can be made by touching a bar of metal or a heavy copper 
wire to the clean spot on the rail and to the tread of the wheel. 
The car will then start. Pouring water on the track may be 
enough to form a ground. If the ground is made with a wire or 
bar as described, the rail must first be touched, and then the 
wheel. The connection must be firmly held in place, or a shock 
will result. The motorman can shut off the power an instant to 
permit the bar or wire to be removed. The use of a thick glove, 
cap, or piece of heavy cloth for holding the connecting piece is ad- 
visable or imperative. 
Refusing to Start.— If a car refuses to start with a good 



THE ELECTRIC RAILWAY. 599 

ground, it may indicate that the rail bonds are gone. The rails 
can be connected electrically with a piece of wire attached in any 
way that seems best. Even a few nails may be driven between 
the ends of two rails to give some attempt at a connection. 

The lightning arrester may be a source of trouble. If dirt gets 
into it, it may establish a ground, and so short-circuit all the car 
connections between it and the motors. This may be of such low 
resistance as to melt the fuse. If cleaning the arrester is not 
possible, it may be disconnected, or its ground wire may be re- 
moved or disconnected. A lightning arrester making ground will 
blow out the fuse when the controller handle is in the off posi- 
tion. This is one way of recognizing it. 

Fuses. — If the fuse blows when the car starts, it may be due 
to so great a load that the armature turns abnormally slow, and 
generates insufficient counter electromotive force. If the brakes 
are set, or if a quantity of dirt has wedged in between brake shoe 
and wheel, the load on the motors may be increased thereby, so as 
to burn out the fuse. 

Another cause for a fuse blowing out is the grounding of the 
field coil of a motor. The cure is to cut out the motor. Short- 
circuiting of field or armature will do the same. Loose or bad 
contacts at the ends of the fuse may help to blow it out. The 
contact pieces at the ends of fuses should be bright and clean, as 
should the surfaces to which they are secured. Sandpapering or 
scraping may be resorted to if necessary. Screws holding fuses 
should be screwed down hard, and should be watched if they are 
liable to become loose. 

Never put in two fuses in place of one or a fuse heavier thaji 
the standard, as it might result in a burned-out armature or in- 
jury of wires or other connections from overheating. 

Examining Connections.— If electrical connections have to be 
examined, tightened up, or disconnected, either pull down the trol- 
ley pole and tie it down, or open the main circuit switch under the 
platform roof or canopy. Take no risks with a live circuit. 

The lamp circuit may be used to give a clew to electrical trou- 
bles. If the lamps light, then the current is on the line and 
the car has a ground connection. It may be only enough for a 
simall current. While the lamps are burning, turn on the con- 



600 ELECTRICIANS' HANDY BOOK. 

troller. If the lamps are dimmed or go out, it indicates a poor 
ground. There is a possibility of running the car ahead slowly 
and picking up a good ground again. 

Controller Troubles.— Sometimes the car will run with one 
controller and imperfectly or not at all with the Other. A burn- 
out, a broken or loose connection, a bent contact finger, may be the 
trouble, or the motor cutrouts may have dropped out of their con- 
tacts. 

Broken=Down Controller. — If a controller breaks down and the 
cause is not obvious nor easily removed, run with the other com- 
mutator. The car must be run by signal from the front platform 
in this case, the conductor remaining in front to watch the track. 

Motor Troubles may be due to the causes which affect other 
motors, but greater in degree, because of the conditions under 
which railroad car motors have to operate. The carbon brushes 
may not play freely, the commutator may wear uneven or have 
a high bar, the carbon brushes may even be burnt into the 
holders from excessive current. There is every chance for dirt 
and oil to accumulate on the commutator surface. Sparking on 
the commutator when the motor is running may be due to one 
of these causes. Absolute flaming on the commutator indicates a 
broken, short-circuited, or wrongly-connected coil. Such troubles 
should be found out before the car goes into service. 

In the bottom of the controller case are two cut-outs, marked 
motor 1 and motor 2 or equivalently. If a motor is in trouble, 
cut it out with its own cut-out and run carefully with one motor. 
Start the car very slowly and gradually under such conditions. 
On a steep grade it would be well not to stop at all. A short, 
steep grade should in such case be taken on the run. Avoid using 
sand. The point to be remembered with a single motor is to avoid 
running it slowly with the controller turned to high power. 

Emergency Stop.— If the brakes refuse to work, emergency 
methods must be resorted to. They should be avoided if possible. 
There are two. 

Throw off' the power at the controller, reverse the reversing 
lever, and turn the controller to first or second notch. This 
method is quick, but is more of a strain on the machinery than 
the following. 



THE ELECTRIC RAILWAY 



601 



Throw off the power at the controller, open main-circuit switch, 
reverse the reversing lever, and turn the controller handle to the 
last notch. 

Jerking Car. — If a car jerks or bucks, it may be due to water 
and mud which has reached the commutator, a bit of wire may 
have got into the motor case and have short-circuited the com- 




TROLLEY WIRE 

TRACK RETURN 
CIRCUIT 

Fig. 454.— Feeder Connection fob Electric Railway. 

mutator bars, or other short circuit may have occurred. The mo-; 
tor in trouble may be detected by the smell due to overheated in- 
sulation. Cut it out at once and run with one motor. 

Car Heating. — Many uses have been found for electric heating, 
but the expense has restricted its use greatly, and its principal ap- 
plication is in trolley cars. For a car with twelve windows, from 
2000 to 3000 watts are needed to supply the heaters, or about 4 
horse-power. A car stove burns about 33 pounds of coal per day. 




Fig. 455.— Feeder Connection for Electric Railway. 



and the expense of a day's heating with allowance for repairs to 
stoves, removal of ashes, and every incidental expense, was cal- 
culated at 191/4 cents a day, with coal at $2 a ton. The expense of 
electric heating varies from 0.36 cent to 2.41 cents per hour. 
The showing is so favorable only because the electric heating 
system has comparatively few repairs. The heaters are not re- 
moved in summer, and there is little in the way of replacement 
needed. The fuel cost for a stove may be only 1%, cents for a 



602 



ELECTRICIANS' HANDY BOOK. 



whole day; the principal expense is in the labor and repair items. 
Electric Radiators are simply resistance coils of iron wire 
sometimes protected by asbestos or equivalent coating. They are 
placed under the seats, and therefore take no room in the car; 
a stove sometimes takes the room of one passenger. In a crowded 
system the conductor may have to neglect a coal stove, and the 




Fig. 456.— Separate Feeder System for Electric RAiiiWAY. 

passengers may interfere with his giving it proper attention. In 
such cases electric heaters are especially advantageous. 

Power Circuit and Feeders. — There are various ways of ar- 
ranging trolley-line circuits. The simplest consists of a single 




Fig. 457.— Interconnecting Feeder System on Electric Railway. 



wire with the rails as a return. Sometimes feeders are used to 
maintain the pressure. 

One of the oldest ways of using a feeder is to run it along paral- 
lel with the trolley wire, and connect from it at intervals to the 
latter. This is an imperfect system. Nothing is gained by it over 
the results which a single trolley wire of cross section equal to 
that of the two wires would give. A variation on this system is 



THE ELECTRIC RAILWAY. 



603 



to divide the trolley wire into sections, each corresponding in 
length to the distance between feed-wire connections. This makes 
it possible to cut out any section of the road, which might be use- 
.ul in some cases of accident. These systems are shown in the 
cuts. Pigs. 454 and 455. 

A true feeder's action would consist in keeping a definite poten- 
tial on a distant point of a line. The trouble is that if a feeder 
is drawn upon for current, 
its drop increases, and it 
fails to some extent in its 
function. An active feeder 
must act imperfectly. The 
following systems try to 
bring feeder action more 
into play. In Fig. 456 is 
shown a road supplied 
with current as usual 
through its wire, and with 
several feeders carried di- 
rectly from the station 
and connecting at distant 
parts of tl^e line. The 
trolley wire may be di- 
vided into sections, and 
subsidiary feeders may be 
introduced. By intercon- 
necting feeders the system, 
shown in Fig. 457 may be employed. 

Insulators. — These are of the most varied type in the great 
variety of electric railway work now carried out. Fig. 458 shows 
an insulator for carrying the trolley wire. It crosses the bottom 
of the insulator, and the weight is taken by a suspension wire 
from which the insulator is suspended by the double hook on 
its top. At the center of the top is a slot through which the sus- 
pension wire passes. 




Fig. 458.— Trolley "Wire Insulator. 



CHAPTER XXXV. 

ELECTRICAL MEASURING INSTRUMENTS. 

The Galvanometer is an instrument for Indicating the passage 
of a current. If used only as an indicator, it is more properly 
called a galvanoscope. Usually the first nam© is employed. 

Under Ampere's law we have seen the law of the deflection of 
a needle by a current illustrated. If a common pocket compass 
with good enough pivot and bearing is held above a conductor 
through which a current is passing, the needle will be deflected 
more or less according to the strength of the current. The fric- 
tional resistance may be great enough to hold the needle immov- 
able unless a strong current is flowing. Such a compass would 
constitute a galvanoscope. 

To increase its sensitiveness, two things can be done. The 
delicacy of pivoting can be increased. For extreme sensitiveness 
the magnetized needle can be hung at the end of a filament of 
silk instead of being poised on a pivot. To increase the action 
of the current, the conductor can be bent into circular or other 
closed curve, and go completely around the needle once or many 
times. A coil of wire of hundreds of turns may surround the 
needle. Proximity increases the action. The coil may be so 
close to the needle as to just leave it room to turn in. 

A galvanometer as usually constructed consists of a magnetic 
needle and a coil of wire surrounding it. 

Simple Galvanometer. — The simple form of galvanometer 
called originally a multiplier is shown in the cut. Fig. 459. A 
coil of wire wound upon a wooden or pasteboard spool or bobbin 
surrounds a magnetic needle. The instrument must be placed so 
that the coil will lie in the magnetic meridian or nearly north and 
south. The magnet will then lie in the coil in the position 
shown. When a current is passed through the coil, the needle will 

604 



ELECTRICAL MEASURING INSTRUMENTS. 605 

be more or less deflected. On such lines as this many galvanom- 
eters of widely varying sensitiveness are constructed. 

The needle as shown in this connection has an axis fastened to 
it. This may be prolonged upward through the coil, and have 
an index fastened upon it. Then the first movements can be seen. 
Otherwise they would escape notice because the needle is hidden 
by the coil. 

The needle may be above the coil, when it will move in direc- 
tions the reverse of those which it would have if within the coil, 
as shown in the cut. 

Astatic Galvanometer.— Sometimes two needles are used fast- 
ened to a central axis, with north and south poles opposed. This 
construction almost destroys the polarity of the two, and would 




Fig. 459.— Simple GrAiiVANOMETEB. 

completely were it possible to have them of equal strength. If one 
magnet is within the coil, and the other with reversed pole is 
above or below the coil, the deflective action on both will be the 
same. This is because the poles are reversed. 

The cuts. Figs. 460 to 462, show an astatic galvanometer. On a 
frame F is wound a double coil of wire, whose turns lie in a verti- 
cal plane. The astatic needles are shown below the frame, their 
north and south poles being indicated by N N and S S. The 
whole arrangement as set up is shown on the right. A glass shad© 
cuts off all air drafts, so as to prevent irregular movements. 

Fiber Suspension — For sensitive galvanometers a thread or 
fiber is used to suspend the needle. It may be a fine thread of 
silk. It is sometimes a thread of silica. This is made by melting 
a piece of quartz, and diawing from it a fine thread on the prin- 
ciple of spinning glass. Sometimes the point of an arrow is 



m 



606 



ELECTRICIANS' HANDY BOOK. 



touched to the melted quartz and shot from a bow, drawing out a 
thread of quartz which fs so fine as to be almost or quite invisible. 
Reflecting Galvanometer.— The sensitiveness of a galvanom- 
eter could be increased by increasing the length of the index. 
The weight of the index might be a factor which would impair its 
sensitiveness, and it would be affected by drafts of air unless in- 
closed. An index four or five feet long would be impracticable. 





Figs. 460 to 46'i.— Astapic Gal\ anometeiv. 

But a weightless index of any length can be provided by using a 
parallel beam of light. 

A concave mirror will reflect a beam of light, and will produce 
a focal image of the source of light at a distance from itself de- 
termined by the relation of the distance L o to the degree of con- 
cavity or radius of curvature of the mirror. The conditions are 
shown in Fig. 463. s s is the mirror, L the source of light, and Q 
the reflected image thrown upon a screen or scale m m. The 
ray Q o is the weightless index referred to above. In the reflecting 
galvanometer the mirror is attached to the magnetic needle indi- 



ELECTRICAL 31 E AS U RING INSTRUMENTS. 



607 



cated by N S in the diagram. The center of the mirror lies in the 
line of the suspending fiber. The distance Q o may be as great 



3^ 



^ 



•-% 



J 






Fig. 463.— Principle of the Reflecting Galvanometer. 

as desired; the longer it is, the more sensitive will the instru- 
ment be. 

Arrangement of Reflecting Galvanometer. — The diagram, Fig. 
464, shows a lamp in a case, with an aperture m m out of which 




Fig. 464.— Arrangement of Lamp Mibror AND Scale for 
Reelectino Galvanometbb. 

a beam of its light emerges. At 8 is the mirror attached to a 
galvanometer needle. The latter with all other detail is omitted 
from the diagram to avoid complication. At ^ is a long scale. 



608 



ELECTRICIANS' HANDY BOOK. 




Fig. 465.— Arrangement of Lamp Screen 
and scaiie for reflecting galvanometer. 



The light which falls upon the concave mirror at s is reflected 

upon the scale, and a 
focal image of the 
aperture mm is 
produced upon the 
scale. The aperture 
m m may have a ver- 
tical wire across its 
center, which will ap- 
pear as a dark line 
across the spot of 
light upon the screen 
and will serve as the 
index. 

In modern practice 
an incandescent elec- 
tric lamp is often used instead of the oil lamp. In such a case 
the lamp is so placed 
with reference to the 
focal length of the mir- 
ror that its incandescent 
filament is projected 
upon the screen, and 
this image serves as the 
index. 

Referring again to 
the diagram. Fig. 463, it 
will be understood that 
if the mirror S turns 
left-handedly, the ob- 
ject reflected to and pro- 
duced upon the scale t 
will move toward the 
top of the page as shown 
by the dotted line Q o. 

The reverse will occur for t^ .,,^ m 

■ Fig. 466.— Telescope and Scale fob 
a swinging of the mirror p^^ne Mirror Reflecting 

in the opposite direction. Galvanometer. 




ELECTRICAL MEASURING INSTRUMENTS. 609 

In the same cut a lens is shown in front of the lamp. By using 
this lens a plane mirror at S may be used instead of th^ concave 
one, and the dotted lines indicate the direction of the rays of li-ht 
when such lens is used. 

The next cut. Fig. 465, shows how the oil lamp is placed below 
the scale and screened from the observer who is in front of it 
The aperture through which the rays pass is seen. A vertical 
wire is secured across it. 

Translucent Scale.-The diagrams have illustrated the use 
of an opaque scale which the observer looks at directly. Some- 
times a translucent scale is used, the observer being back of it 
and watching the index mark through it 

Plane Mirror Reflecting Galvanometer. -Another arrange- 
ment of the reflecting galvanometer depends upon simple reflec- 
tion of the scale in a plane mirror attached to the galvanometer 
needle. The cut. Pig. 466, shows a telescope mounted on a stand- 
ard with a scale below it. The observer looks directly at the 
galvanometer mirror and sees reflected in it a portion of the scale 
This gives the reading of the instrument. A cross wire, cocoon 
fiber, or equivalent may cross the mirror or be contained within the 
telescope, in order to give a line to fix exactly the scale division 

The Thomson or Kelvin Galvanometer.-The characteristics 
of this instrument are the extreme lightness and small size of 
the moving parts, which are the needle or needles and a mirror 
generally concave. The coil of wire is of rather large diameter 
as referred to the length of the needle. As used, the deflections 
of the needle are so small that the current is sensibly propor- 
tional to the deflections. It is constructed dead-beat, astatic or 
according to any other requirement. 

In one type of instrument four magnetic needles 0.015 inch 
long are cemented to the mirror. The latter is 0.024 inch diam- 
eter, the total weight of mirror and needles being 1 grain The 
object of having several needles is to get the maximum of mag- 
netization with the smallest weight. This reduces momentum 
and makes the combination more dead-beat. 

^ The mirror and needles are suspended by a cocoon fiber, unspun 
silk, and of extreme thinness. The mirror hangs in the center 
of a vertical ring of brass with closed back, and the front covered 



610 ELECTRICIAN^'' HANDY BOOK. 

with a pane of glass. The coil surrounds the ring. A rod rises 
from the ring and carries a curved regulating magnet. 

Regulation of Sensibility. — The regulating magnet is turned 
with its north pole to the south. This counteracts to a certain 
extent the terrestrial magnetism. It is moved up and down until 
its action on the needles nearly deprives them of directive force. 
This is taken as the working position for sensitive work. 

An astatic galvanometer is made on the same lines. Two coils 
wound in opposite senses are ■em.ployed, one above the other. One 
acts on one needle and the other on the second needle, whose 
poles are reversed. The coils are each divided into two parts, 
so that there are really four coils. The connections are arranged 
so that the coils can be connected in various ways. 

In some very accurate observations the scale is placed 20 feet 
from the mirror of the galvanometer. This is equal in sensitive- 
ness to an index 40 feet long. 

A small form of the Thomson or Kelvin galvanometer is shown 
in Fig. 467. 

Tlie Ballistic Galvanometer is used to measure the quantity 
of electricity in an instantaneous discharge. In use the dis- 
charge is passed through its coils, and the extreme deflection of 
the galvanometer is noted. 

Various types can be employed. Ayrton and Perry have thus 
modified the Thomson galvanometer for ballistic work. Forty 
little magnetic needles of different lengths are, with the aid of 
segments of a hollow lead sphere, mounted as two spheres. The 
spheres are joined by a rigid rod astatically, or with the magnet 
poles pointing in opposite directions. The combination is sus- 
pended in place of the usual mirror and needles by a fiber. The 
galvanometer is very sensitive, and the air offers little resistance. 
It is corrected as follows: Call a' the first throw and a" the 
second throw on the same side of the zero mark. The arc a, 
which would have been attained by the first throw without the 
resistance of the air, woul4 be expressed by the formula: 

, , a' — a" 

a =: a -t . 

4 
The extreme limit of an oscillation is called its elongation or 

instantaneous deflection. 



ELECTRICAL MEASURING INSTRUMENTS. 



611 



The Depre2=D'Arsonval Galvanometer is much used for bal- 
listic work. The cut. Fig. 468, shows the construction of a simple 
form. 

A strong horseshoe permanent magnet is mounted on a base- 
board, its poles projecting directly upward. A rectangular coil 
of No. 40 silk-covered copper wire is the moving element. This 
is held symmetrically between the poles of the magnet. The 
magnet in the instrument we are describing is 7 inches high, and 





Fig. 467.— Sir William Thom- 
son's OB, Kelvin Beflect- 
iNG Galvanometer. 



Fig. 468.— Deprez-D'Abson- 

VAL GALVANOMETEE. 

Original Form. 



is formed of three magnets each 1^4 inch thick and bolted to- 
gether. The coil of wire is 2i^ inches long internally and 1^^ 
inches in internal width. Within the coil a hollow soft-iron 
cylinder is supported by an arm projecting from a standard at 
the back of the baseboard. The cylinder is a fraction of an inch 
smaller than the coil in all directions, so as to fit within it without 
touching it. Its sides are about 3-32 inch thick. The coil is sus- 
pended by a hard-drawn silver wire No. 32 or 0.008 inch diameter. 
A similar wire connects the center of the bottom member of the 
coil to the base. The current goes through the coil, entering 



612 



ELECTRICIANS' HANDY BOOK. 



by one silver wire and passing out by the other. The resistance 
of the coil is about 150 ohms. A concave mirror is attached to 
the suspension hook directly above the coil, moving with it. 
Sometimes the wires are strained, and sometimes the lower wire 




Fig. 469.— Deprez-D'Absonvai, Galvanometer. 



is left loose. In the latter case, as far as the action of the in- 
strument is concerned, it is only a conductor for the current. 

A modern form, as made by Leeds & Northrup of Philadelphia, 
is shown in Fig. 469. The coil and core are seen best in the left- 
hand figure, showing the suspension element removed from the 
magnet and with its glass front taken off. 



ELECTRICAL MEASURING INSTRUMENTS. 613 

Ballistic fleasurement. — The ballistic galvanometer is used 
to determine the quantity or coulombs K of electricity which pass 
through its coils during a very short discharge. If the galvanom- 
eter needle moved as the discharge passed, it would receive a 
weaker' and weaker current as the discharge approached its end. 
In such a case the motion of the needle or other movable element 
of the galvanometer would not tell anything, as there would be 
no practicable way of running up or integrating its motions. But 
the whole discharge may be completed before the needle begins 
to move. When it does move under such condition, the motion 
represents the sum of all the actions which have been exerted 
upon it, whether great or small. The needle under their com- 
bined effect will be deflected suddenly, and the limit of its throw 
will depend upon the sum of these forces. 

If the charge passes before the needle begins to move, one 
ballistic condition will be present. 

The motion of the galvanometer indicator may be checked or 
damped by air resistance or by magnetic induction. Another con- 
dition for the ballistic galvanometer to fulfill is that this shall 
be very small. 

Generally, a reflecting galvanometer is employed for ballistic 
work. Its reflected light spot is received upon a scale four feet 
or more distant. 

Let K indicate the coulombs which produce an instantaneous 
throw of Jc° by ballistic action. Let A indicate the amperes of 
current which would produce the steady deflection a°. Let P 
be the time of vibration of the galvanometer in seconds. When 
k° and a° are both small, the law of the deflection under ballistic 
conditions as given above is: 

P sin - 



K = -- X A X 



^ tan a" 

The angle of deflection a° for a given current A amperes must 
be small. The angle k° must also be small to keep the light spot 
upon the board. Thus, if the scale board is 4 feet distant from 
the mirror of the galvanometer, a deflection of 2 feet corresponds 
to an angle of less than 30°. 

If the scale is divided into equal divisions, they may be read 



614 ELECTRICIANS' HANDY BOOK. 

and used instead of angular deflections. Then if we part from 
degrees and call the two kinds of deflections k and a respectively, 
we may greatly simplify the formula and let it read thus: 

This will give a result very nearly accurate. 

A galvanometer for ballistic work should be of slow periodicity, 
as P has to be determined, and it is more accurately determined 
if it is a long period. A heavy moving element, whether needle 
or coil, lengthens the periodicity and also makes the needle 
slower in starting, which is a favorable condition. 

A usual method of working is to reflect a lighted incandescent 
lamp fllament from the mirror, and to receive its image upon a 
strip of grqund glass, through which the ignited filament shows. 
Before making a test the galvanometer must be absolutely at 
rest. This condition is disclosed by the image of the filament 
appearing motionless on the scale. 

It is impossible to measure with accuracy the time of a single 
swing of the needle or coil of the galvanometer. For this deter- 
mination the needle is set swinging, and the time of ten or more 
swings is taken. Dividing the time by the number of swings 
gives the periodicity P of the instrument. 

Ballistic Calculation.— The following example is taken from 
Ayrton's "Practical Electricity": 

"With a galvanometer, the needle of which executes eleven 
complete swings in 6% seconds, 1 Daniell's cell, having an E. M. 
F. of 1.07 volts and an internal resistance of 3 ohms, produces a 
constant deflection of 127 scale divisions when there is a resist- 
ance of 10,000 ohms in the circuit, excluding the galvanometer, 
v/hich has a resistance of 7,500 ohms, and which is shunted with 
the one one-thousandth shunt. What number of coulombs is 
discharged through the galvanometer when an instantaneous 
deflection of 230 = k scale divisions is produced? 

The solution is as follows: The periodicity P of the galvanom- 

6 5 
eter is — or 0.59. The current in amperes A producing the de- 
ll 

E 
flection 127, which is a, is found by Ohm's law, I = — . 



ELECTRICAL MEASURING INSTRUMENTS. 615 

The resistance of the battery is 3 ohms, that of the resistance 
coil is 10,000 ohms. The resistance of the galvanometer and the 

7t''0 
shunt in parallel with it is J — — or 7.560. But as the shunt in 

luUU 
parallel with the galvanometer passes 0.999 of the current, one- 
one-thousandth of the current goes through the galvanometer 

1.07 1.07 



coils. The total current is therefore 



3 + 10,000 + 7.56 ~ 10,000 



approximately. As of this current acts upon the galvanom- 

1000 

1.07 
eter, because of the shunt the current A is in qqq qqq ampere. 

Returning to our formula and substituting these values, we 
have: 

_0^ 1.07 230_ 

^- 7t ^ 2 X 10,000,000 ^ 127 
which gives as answer 0.01822 micro-coulomb. 

The answer, it will be observed, is given in micro-coulombs. 
This is done to avoid the six more decimal places which would be 
required were the answer given in coulombs. The above might 
have been put thus: 



Micro-coulombs 



59 1.07 230 



X ^ .. ,n X 



7t ^ 2 X 10 -^^ 127 
The Tangent Galvanometer is an instrument whose deflec- 
tions can be interpreted to give directly the intensity of the cur- 
rent which passes through them. Its construction is based on 
the following principle: If a magnetic needle is placed in a uni- 
form field of force due to a current, which field is at a right angle 
to the terrestrial field, it will be deflected at an angle greater 
or less as the strength of the field is greater or 1-ess. The law 
of the deflection will be that the tangent of the angle of deflection 
will be proportional to the strength of the current producing the 
field. 

The construction of the tangent galvanometer is shown in the 
cut. Fig. 470. A ring of large diameter stands vertically on a 
support. The current whose intensity is to be determined passes 
directly through an insulated conductor wound around the ring. 
For heavy currents a single turn of wire would be sufficient. A 



616 



ELECTRICIANS' HANDY BOOK. 



magnetized needle is supported at the center of the ring. The 
needle must he as short as possible. For a ring 12 inches in 
diameter, a needle 1 inch long may be used. As the needle will 
be too short to admit of a scale being used large enough to give 
good readings, a very light index is attached to it, which index 
is several inches long. A dial of corresponding diameter is 
under the index. 

The dial can be graduated in de- 
grees. Then a reference to a table 
of natural tangents will give the rela- 
tive value of the current intensity 
producing any given deflection. The 
dial can also be graduated so as to 
give tangent readings. Thus, the tang- 
ent of 5° is 0.08749, that of 10° is 0.1804, 
that of 15° is 0.268, and so on. A 
direct-reading tangent scale might 
have the reading 8.75 correspond to 
its 5° point, with the intermediate 
ones filled in. The numbers put upon 
the scale would be integral ones, 
starting from 1 and extending on 
either side of the zero point. 

The angle of 45°, whose tangent is 
equal to unity, would on the above 
basis be marked 100. The point of 
maximum sensitiveness is at 45°. 

The tangent galvanometer must be 
placed in the plane of the earth's mag- 
netic meridian when it is to be used on the tangent pri nciple. 

This instrument is sometimes called the tangent compass. 

The 5ine Galvanometer is a galvanometer whose indications of 
strength of current passing vary with the sine of the angle read 
off its scale. It has a vertical coil with a magnetic needle in the 
center pivoted so as to rotate in a horizontal plane. Thus far it 
resembles the tangent compass. In use the coil is turned into 
the plane of the magnetic meridian, as shown by the magnetic 
needle. The current is then turned on and the needle is deflected. 




Fig. 470. 



-Tangent Galvan- 
ometer. 



ELECTRICAL MEASURINa INSTRUMENTS. 617 

The coil is turned in the direction of the deflection, following the 
motion of the needle, which still moves a little as the coil ap- 
•roaches its plane of position. Eventually the coil is brought 
iccurately into line with the needle, and the angular deflection 
from the original position or zero point is taken. The strength 
of the current is proportional to the sine of this angle. 

The proportions of length of needle to diameter of coil are 
without effect on the exactness of the sine law. The coil can 
be made of small relative diameter compared to that necessary 
in a tangent compass. This increases the sensitiveness. The 
sensitiveness also increases with the angle of deflection. 

This instrument is also called the sine compass. 

The Thomson or Kelvin Absolute Electrometer is based upon 




Fig. 471.— Sir William Thomson's Absolute Electrometer. 

the attraction exercised between two electrifled surfaces. An 
insulated metallic disk is hung from one end of a balance beam. 
It hangs horizontally in an opening in a larger annular metallic 
plate called the guard ring, which is also insulated. Sometimes 
it is suspended by a spring. When uncharged it hangs a little 
above the plane of the guard ring. Below the annular plate, a 
little distance from it and parallel with it, is another insulated 
metallic plate in electrical contact with the movable plate. The 
cut, Fig. 471, shows the disposition of parts. 

The principle is that two surfaces oppositely electrifled attract 
each other with a force proportional to the square of the electro- 
motive force between them. When an instrument of this de- 
scription is calibrated for direct current, it can be used for 
alternating currents, and will indicate their effective values. 

To use it, the terminals whose potential difference is to be de^ 



618 ELECTRICIANS' HANDY BOOK. 

termined are connected, one to the lower plate and the other to 
the suspended plate. The force with which they attract each 
other is determined by weighing it, if a balance, or by deflection 
of the spring, if the spring construction is employed. The mov- 
able plate must be brought to accurately lie in the plane of the 
guard ring. The distance between the upper and lower plates 
must be accurately known. The guard ring and circular plate 
must be of identical potential, and this is why they are in electri- 
cal connection through the suspension rods or spring carrying 
the movable plate. 

Let E= electromotive force between the upper and lower plates. 
d = the distance between the same. 
F = the attraction between the plates in dynes. 

(1 dyne = 1 —1 gramme) 
a = the area of the movable plate in square centimeters. 
Then B'' - ^ao.OOOd^F 
a 
Another method of using it is to keep the upper plate at a con- 

stant potehtial by some source of constant electromotive force, 
which may be a small influence machine, somewhat on the Wims- 
hurst type. The lower plate is alternately connected to the earth 
and to the terminal whose potential is to be measured. Each 
time the connection is made, the attraction of the disk for the 
lower plate is determined. The difference between the potentials 
of earth and terminal gives the potential of the body referred to 
the earth. 

Qalvanometer Shunts. — A galvanometer may be too sensitive 
for some specific test. The voltage may be sufficient to pro- 
duce a current which would throw the light spot off the scale, or 
which would deflect it so nearly to 90° as to make its readings 
worthless. A right angle or 90° is the limit of motion of a gal- 
vanometer needle, and in the neighborhood of 90° its readings 
are very inexact. Thus a galvanometer too sensitive for the 
work it has to do would have its needle deflected so nearly over 
90° that it would lose accuracy. If the current is split up, and 
only a portion is passed through the coils of the instrument, it 
can be reduced in sensitiveness so as to bring the readings within 
a good working portion of the scale. To split up the current. 



ELECTRICAL MEASURING INSTRUMENTS. 



619 




a known resistance is connected across the galvanometer term- 
inals, so as to be in parallel with the coils. These resistances are 
definite fractions of the resistance of the galvanometer coil. 
They are termed galvanometer shunts. 

A galvanometer shunt, such as supiDlied by instrument makers, 
is shown in Fig. 472, and the diagram. 
Fig. 473, shows the connection and its re- 
lation to the galvanometer. It will be 
seen that it is in parallel with the instru- 
ment, and passes a fraction of the total 
current, whose value depends on the rela- 
tive resistance of the galvanometer and 
of the shunt, as explained below. 

To reduce the sensibility of the gal- 
vanometer to l/n of its normal value, the 
resistance must be equal to that of the 
galvanometer g divided by w — 1. Sup- 
pose that a shunt box is used which can re- 
duce the sensibility to 1/10, 1/100, and 
1/1000 of the normal value. Then the re- 
sistances of the three shunts are g/d, g/2d, 5^/999, calling g the 
resistance of the galvanometer. 

When a shunt is put in parallel with a 
galvanometer, the proportion of the total 
current which passes through the gal- 
vanometer is equal to the quotient obtain- 
ed by dividing the resistance of the shunt 
by the combined resistance of the two 
pieces, galvanometer and shunt. This quo- 
tient multiplied by the total current gives 
the galvanometer current. 

The resistance of the galvanometer and 
shunt is equal to the product of the resistances divided by their 
sum. 

Compensating Resistance — When a galvanometer is shunted, 
the decrease in resistance causes an increase of current. A re- 
sistance in series, called compensating resistance, is used to bring 
the current back to its former strength. The compensating re- 



FiG. 473.— Galvano- 
meter Shunt. 




Fig. 473.— Shunted 

GrALVANOMETEB. 



620 ELECTRICIANS' HANDY BOOK. 

sistance is equal to the square of the galvanometer resistance di- 
vided by the sum of its resistance and the resistance of the shunt. 

Constant of a Galvanometer. — The French constant is the de- 
flection produced in a galvanometer by a Daniell's cell in a cir- 
cuit of total resistance of one meg-ohm or one million ohms. 
The resistance of the battery and galvanometer are included. In 
England the constant of a galvanometer is the number by which 
its indications must be multiplied to reduce them to a given unit 
of current. 

Another form of galvanometer constant applicable to tangent 
galvanometers is used in England. 

Let n = number of turns of wire in the coil. 
r = radius of coil. 

Then 

constant = — ~ — 
2 7t n 
It appears in the following formula: Let 
H =: horizontal component of earth's magnetism in dynes. 
1 1= current intensity in C. G. S. units. 
S = angle of deflection of needle. 
n and r = values given above for them. 
Then: 

1= - X H tan S. 

2 Tt n 

And this value multiplied by 10 will give the current in 
amperes. 

A still more general definition of the working constant as used 
in every-day practical work in this country is the following: 

The working constant of a galvanometer is the number of scale 
divisions of deflection that would be obtained by causing the cur- 
rent from the given battery to pass through the galvanometer 
and a resistance of one meg-ohm. 

Determination of the Constants — Galvanometer constants as 
used in France, England, and America vary because it is an 
arbitrary working figure only. Its determination for practical 
use is now to be described. 

In the diagram, Fig. 474, G represents a galvanometer, B a bat 
tery, S the galvanometer shunt, and R a known resistance. Sup- 



ELECTRICAL MEASURING INSTRUMENTS. 



621 




pose the shunt to be fir/999. This reduces the sensibility of the 
galvanometer to 1/1000 of its normal sensibility. Suppose the 
resistance R to be 100,000 ohms. When the circuit is closed, the 
galvanometer will be deflected. Without the shunt the deflection 
would be theoretically 1000 times as great, on the assumption that 
the deflections vary as the current. This assumption only holds 
true for very small deflections in reality, and is applicable in 
this case because in the actual test deflections within this limit 
are used. 

The shunt makes the deflection 1/1000 as great as if there were 
no shunt there; the resistance makes it 10 times as great as if a 
meg-ohm (1,000,000 ohms) were the resistance instead of 100,000 

ohms. Therefore, for a meg- 
ohm resistance and without 
any shunt the resistance would 
be equal to that shown multi- 
plied by 1000 and divided by 
10. 

The general rule for deter- 
mining the working constant 
with the connections shown 
in Fig. 474 is as follows: 
The working constant is equal to the product of the deflection 
of the galvanometer multiplied by the multiplying power of the 
shunt, and by the meg-ohms resistance in series with it. 

In the case cited the multiplying power of the g/999 shunt is 
1000, the meg-ohm resistance in series is 1/10 meg-ohm. The de- 
flection is multiplied by 1000 X 1/10. 

Suppose a deflection of 250 scale divisions was given with the 
resistance and shunt as above. The constant would be: 
250 X 1000 X 1/10 = 25,000. 
Such would be the constant for a D'Arsonval galvanometer with 
40 or 50 volts battery. As high a constant as 2,000,000 can be 
obtained for laboratory practice. 

A battery giving 50 volts is enough for ordinary work. By 
increasing this voltage the deflection is increased, and conse- 
quently the galvanometer constant is also increased. In deli- 
cate work a potential of 600 volts is sometimes used. In ordi- 
nary work 100 volts is not excessive. 



Fig. 474.— Determination of the 
Galvanometer Constant. 



622 



ELECTRICIANS HANDY BOOK. 



Figure of Merit.— This is the resistance of a coil placed in 
series with a galvanometer, so that a potential difference of one 
volt will produce a deflection of one division on the scale. 

Sometimes a Daniell cell (E = 1.07 volt) is taken as giving 
the potential for the figure of merit. Properly, the entire re- 
sistance of the circuit should give the figure of merit, not merely 
that of a Resistance coil in series with the line. But in practice 
the resistance of the galvanometer coil so far exceeds that of 





Fig. 475.— Siemens's Dynamometer. 



Fig. 476.— Connections of 
SiEMENs's Dynamometer. 



the rest of the circuit that it can sometimes be used directly with- 
out adding in the rest of the resistances. 

Galvanometer Resistance.— For thermo-electric work a gal- 
vanometer of about % ohm resistance is used. Thomson's gal- 
vanometers have from 5,000 to 10,000 ohms resistance, with be- 
tween 2 and 3 miles of wire 0.004 to 0.008 inch diameter. Some 
galvanometers wound with German-silver wire have 50,000 ohms 
resistance, and a single Daniell's cell through 20 meg-ohms re- 
sistance will move the index through 200 divisions of the scale. 
Siemens's Dynamometer,— This instrument, whose construction 



ELECTRICAL MEASURING INSTRUMENTS. 623 

is as simple as its theory, is the standard instrument for meas- 
uring alternating currents. It is shown in the cut, Fig. 475. ' A 
fixed coil of a number of turns of wire, 55 in one pattern, is 
mounted immovably as shown. The axis of its central opening 
is horizontal. A movable coil surrounds the central immovable 
one. The latter has comparatively few turns — often it has only 
one. The relation of the two coils is shown in Fig. 476, in which 
A, B, C, D represents the immovable coil, and E, F, G, H the mov- 
able one. The current enters at D or G, and passing through both 
coils in series, as shown, establishes fields, which tend to pull 
the coils into parallelism. The movable coil has its two lower 
terminals one above the other in line with the spring suspension. 
S at K, and the three points are exactly in the axis of the coil, so 
that it is free to rotate under the smallest force. On this free- 
dom depends its sensitiveness. 

Near the base of the machine is a mercury cup, and imme- 
diately below it is a second one. The ends of the movable coil 
dip into these cups, which are vertically over each other. The 
current, entering by a binding post, goes through the immovable 
coil and then to one of the mercury cups. Passing through the 
movable coil, it enters the other mercury cup, which is connected 
to the other binding post, by which the current leaves the instru- 
ment. Thus the coils are connected in series with each other, and 
the entire current to be measured goes through each. 

The movable coil is kept in a vertical position by a spiral 
spring. The axis of this spring is vertical, it is fastened to a 
bracket directly over the mercury cups, and its lower end by a 
wire is connected to the center of the upper bend of the movable 
coil. Above the spring is a horizontal dial. A handle to which 
the spring is attached rises from the center of the dial, and an 
index is attached to it. By turning the handle the index can be 
moved over the face of the dial like a hand of a clock. The dial 
is graduated around its edge. 

A second index rises from the movable coil, passes by the edge 
of the dial, and is bent over across the graduated scale on the 
dial. Its position can thus be determined by the zero point on the 
scale. A plumb bob or level is used to set the instrument level, 
and sometimes connections are supplied, so that different numbers 



624 ELECTRICIANS' HANDY BOOK. 

of turns of wire of the fixed coil can be thrown into the circuit. 

Normally, when the index on the handle is set at zero, the in- 
dex of the coil will also be there, the points of the indices facing 
each other and coinciding in angular position. This is when no 
current is passing. The coils will then be at right angles to each 
other, and the spring will be without any torque or turning force 
(moment). If a current is passed, the movable coil will tend tO' 
turn and place itself parallel to the other one. By turning the 
handle this tendency is resisted, and the coll index is brought back 
to zero. This strains the spring, which now exercises torque equal 
to that of the coil. The angle through which the index of the 
spring is turned is proportional accurately to the square of the 
current, whether it is an alternating or direct current. This is be- 
cause of the law that the action between two coils such as those 
of the dynamometer is equal to the product of the currents pass- 
ing through them. But as these coils are in series, the product 
of the currents is the square of the current. 

This instrument is as far as the coils are concerned a zerO' in- 
strument. Its indications depend on the values of the squares 
of the deflections of the spring index. Hence if it is calibrated 
by passing a single current of known value through it, it is cali- 
brated for all currents within its range of action. 

The advantages of the instrument are several. The parts act- 
ing on each other occupy exactly the same relative positions 
when the reading is taken. Another is that it contains no per- 
manent magnet. The field established by such is liable to change, 
although as magnets are now made by makers of reputation, 
there is little danger of any such change. Its simplicity and 
approach in action to being an absolute instrument are also ad- 
vantages. 

Sometimes two stationary coils are used of different number 
of turns, and one or the other is used according to the current to 
be measured. 

The instrument should be set up so that the 0° diameter of the 
%cale coincides with the magnetic meridian of the earth. This pre- 
vents it from being acted on by the earth's magnetism. 

Rheostats. — An early form of resistance for use in experi- 
mental work is the rheostat. It is still in extensive use in labor- 



ELECTRICAL MEASURING INSTRUMENTS. 



625 



atories. It consists in its most usual type of construction of a 
bare wire, often of iron or German silver, which is wound 
around a cylinder. If the cylinder is of metal — and it is often a 
piece of wrought iron pipe — it must be insulated from the wire. 
Asbestos paper is a good material for this purpose. The wire is 
wound around it, with the turns as close to each other as pos- 
sible without touching each other. One end of the wire is con- 
nected to the circuit. The other terminal of the circuit is con- 
nected to a sliding contact, which latter is mounted on a bar, so 
as to slide longitudinally up and down the cylinder making con- 




FiG. 477.— Laboratory Rheostat. 

tact with the wire. The farther it is placed from the end connect- 
ed to the circuit terminal, the more of the wire will be thrown 
into the circuit; and the greater this length of wire is, the greater 
the resistance is also. As described, the wire is brought into the 
circuit one turn at a time. By mounting the cylinder so as to 
rotate, the wire can be brought into circuit a fraction of an inch 
at a time. 
^ Many varieties of the rheostat have been constructed. 

The cut. Fig. 477, shows a very delicate rheostat for use with a 
potentiometer or similar apparatus. A helical line on the sur- 
face of the cylinder shows where a wire is secured. The small 
screw projecting from the center of the apparatus carries an arm, 



626 



ELECTRICIANS' HANDY BOOK. 



which has a contact point which can be brought in contact with 
any part of the wire. As shown in the cut, a scale is seen on the 
left. This reads one division for each turn of the handle. The 
screw rising from the center is of the same pitch as that fol- 
lowed by the wire on the drum. A circular scale on the upper 
edge gives the fractions of a turn. The position of the handle 
determines the point of contact with the wire. The position of 
this point brings an amount of the wire indicated by the reading 
of the two scales into the circuit. The resistance of all the wire 

being known, the resistance of 
the fraction is calculated. 

Resistance Coils.— A resist- 
ance coil is made of a length 
of insulated wire of known 
resistance. As the wire may 
be of very great length, it is 
coiled compactly. To avoid 
inductance it is doubled be- 
fore coiling. The current goes 
through one half of the coil in 
one direction and through the 
other half in the other, and 
the two inductances counter- 
act each other almost perfect- 
ly. Insulated German-silver 
wire is a usual material for 
change of resistance by tem- 




FiG. 478.— Arrangement of Resist, 

ANCE COIIiS, 



Of 



low. other alloys are used by 



the coils, as its coefficient 
perature variations is very 
different makers. 

Resistance Boxes. — A quantity of such coils are mounted in a 
single box called a resistance box. The resistance box should have 
the following qualities: Accuracy of adjustment, dependent on 
the individual coils being correct, and small sensibility to changes 
of temperature, dependent on the alloy of which the wires are 
made. The wire should be double silk-coated. The doubling of 
the wire and its connection to contact blocks on the top of the 
box is shown in Fig. 478. 

The wire is wound on spools or reels. Some makers use thin 



ELECTRICAL MEASURING INSTRUMENTS. 627 

brass reels to facilitate cooling; others use ebonite or parafRned 
wood for the reels. The wire is liable to be heated by the passage 
of a current, and it is this heating which the brass reels are in- 
tended to dispose of. Wire is wound on each coil until the desired 
resistance is attained, the last corrections are applied, and it is 
then steeped in melted paraffin wax. The resistance of a wire is 
changed by bending. It is therefore necessary to test the resist- 
ance of the coil after it is wound. The object of the paraffin 
wax is to exclude moisture. 

Resistance Wire.— A typical composition of German silver is 
the following: Copper, 50 parts; zinc, 30 parts; nickel, 20 parts. 
All parts are parts by weight. 

The resistance of the wire is increased by increasing the per- 
centage of nickel. The wire should be well annealed to make it 
as soft as possible. 

The British Association Standard Ohm.— The alloy adopted 
for this standard was either German silver or an alloy of two- 
thirds silver and one-third platinum by weight. 

Arrangement of Coils. — On the top of a resistance box are 
seen a number of blocks of brass. To each block two terminals 
are connected by tapping into sleeves or into the undersurface of 
the block, and by soldering. One is a terminal of one coil, and 
the other that of its neighbor. Grooves are made in the vertical 
sides of the - blocks facing each other. These are accurately 
reamed out to fit the slope of brass plugs with insulating handles. 
Referring to Fig. 478, it will be seen that if a plug is inserted, the 
coil beneath it will be short-circuited or cut out. Numbers mark- 
ed on the top of the box indicate the resistance of each coil below 
the number. The resistance of a box with the plugs out is equal 
to the sum of the resistances marked on its top. Frequently there 
is a pair of blocks, which if unplugged cut out the whole set of 
coils. This is often called the infinity hole or plug. 

The cut. Fig. 479, shows the top of a modern resistance box. 
The Wheatstone bridge box is merely a special form of resistance 
box with the coils arranged for convenient bridge operations. 

The order of resistances of the coils varies according to the 
ideas of the makers. 

Siemens's Plan is one of the oldest arrangements of resistance 



628 



BLEGTmCIAl^^' HANDY BOOK. 



coils in a resistance box. A series of coils are arranged between 
blocks. The successive values of the coils are 1, 2, 4, 8, 16, 32, 
etc., as far as desired. By plugging between all the coils, the re- 
sistances are all short-circuited. By removing any single plug 
the resistance named above it is thrown into circuit. Starting 
at the left, taking out the first plug throws in 1 ohm; taking 
out the second throws in 2 ohms, giving a total of 3; taking 
out the third also throws in a total of 7, and so on. By taking 
out any number of plugs, whether consecutively or not, the sum 
of the resistances marked will be thrown into the series. The 




00(S)0( 



5000 2000 1000 1C00 500 200 100 ^100 | O 

:©) 3CZ)i3CZ)(Z)OCDQCJ 



Fig. 479,— Top of a Wheatstone Bridge Resistance Box. 



combination is very interesting, but it is obsolete, as it does not 
lend itself to easy decimal summation. 

Modern Arrangements. -The following are approved systems of 
resistances for 16-coil boxes. It will be seen that any number of 
ohms down to units can be obtained by different combinations: 

(a) 1, 2, 2, 5, 10, 10, 20, 50, 100, 100, 200, 500, 1000, 1000, 2000, 
5000. 

(Z>) 1, 2, 3, 4, 10, 20, 30, 40, 100, 200, 300, 400, 1000, 2000, 3000, 
4000. 

(c) 1, 1, 3, 5, 10, 10, 30, 50, 100, 100, 300, 500, 1000, 1000, 3000, 
5000. 

The easiest way to plug in a resistance is to start with all the 
plugs in place. A glance at the figure indicating the ohms desired 



ELECTRICAL MEASURING INSTRUMENTS. 



629 



will show what plugs to remove to make the sum of resistances 
thrown in equal thereto. 

A disadvantage is to be found in this type of arrangement. A 
plug is needed for every coll, and when a number of coils are 
cut out, a quantity of plugs equal to their number must be used. 
A single badly-placed plug will introduce unknown resistance. 
The trouble is emphasized by the fact that this last is most apt to 
occur when the greatest number of plugs are in place. This is 
when the resistance is lowest and when any additional resistance 
will be the largest per cent of the total. 



Tjf-A/S 



WMUUmUUL 



A? /<? /0 



/o /a /a /o /o /Q- 




Fig. 480.— Decade Plan of Resistance Box. 



The Decade Plan is an improvement that has been recently 
introduced. The diagram. Fig. 480, shows one of the arrange- 
ments. 

The lower set of coils are of one ohm resistance each and con- 
nected in series. Each block has a plug groove in its side facing 
outward. A long bar of brass is mounted opposite the row of 
plugs, with grooves in it corresponding to those in the blocks. 
The next row of coils are of 10 ohms resistance each, and are 
arranged in series with blocks. A long brass strip is provided 
for them also. The connections for the circuit are marked + and 
— • in the diagram. 

In the above arrangement a single plug inserted in a hole be- 
tween block and bar will give any value in a decade. Thus the 



630 



ELECTRICIANS' HANDY BOOK. 



/ 



(/) 



NAAAA/VWVV>™ -h 
WWVWVWVi 



3' 

f\AAAAAAAAA/ 



'K^) 



two plugs indicated by the black spots give 35 ohms resistance. 
No more plugs than these two are ever needed for this box. There 
is less danger of losing plugs, of loose contact^, and of straining 
the junction of the brass blocks and the hard-rubber box top. 
The latter trouble sometimes leads to warping the rubber, as the 
plugs are forced down between the blocks. The decade plan 
lends itself to the use of sliding contacts, either on a straight 
line or arranged dial fashion. This substitute for plugs is com- 
ing into use. 

The number of coils used on this system is rather large. The 
Leeds & Northrup Company have other combinations, of which 

the following, Fig. 481, is an ex- 
ample. A 1-ohm, 3-ohm, 3-ohm, 
and 2-ohm coil are arranged in 
series as shown. The terminals 
are indicated by + and — . If 
1 and 5 are connected, the resist- 
ance will be zero. If 2 and 5 
are connected, only 1 ohm will 
be left in circuit. If 4 and 1 are 
connected, 2 ohms will be left in 
circuit. By following this out, 
it will be found that every re- 
sistance from 1 ohm to 9 ohms 
can be given by these four coils. 
By the block and plate arrangement a single plug does all the 
connecting for the nine values of the four coils. 

The above arrangement takes care of each decade with only 
four coils and one plug to the decade. 

Details in the Construction of Resistance Boxes.— The 
hard-rubber surface must be clean to avoid a diminution of re- 
sistance; therefore all parts of the rubber must be accessible 
for cleaning. A defect in some constructions of resistance boxes 
is that the surface of the rubber between the pairs of blocks can- 
not be conveniently got at for the removal of dust. The plugs 
should go down below the shoulder or top of their tapering ends 
to avoid the formation of ridges by wearing and friction against 
the edges of the contact blocks. 



w 




{5) 
Fig. 481.— Decade Plan for 
Resistance Box. 



ELECTRICAL MEASURING INSTRUMENTS. 631 

Shellac for coil insulation is now preferred by the best makers 
to paraffin. It is put on in solution, dried and baked. Wire with 
a low-temperature coefficient must be used for the coils. The 
baking of the shellacked coils tends to equalize the winding 
strains and to artificially age the wire. Metal spools by their 
better cooling powers have the effect of reducing temperature 
errors and changes. 

Metal Spools are made by Leeds & Northrup in two parts, be- 
ing divided longitudinally. The halves are insulated from each 
other, and secured together by rings of insulating material at 
top and bottom. The spool is covered with silk, shellacked, and 
wound with the wire. Each half of the tube is connected to its 
own contact block or plate, and the ends of the wire are soldered 
each to one-half of the spool. Thus there are no long ends of 
wire to be disposed of, and connecting the spool to its holding 
bolts or studs connects at the same operation the ends of the 
coil. 

Practical Notes. — The plugs must be perfectly clean. In con- 
structing the box, the taper of the plugs must match that of 
the holes. Filing and rubbing with fine emery paper is some- 
times recommended, but such treatment should be sparingly used, 
as it will tend to spoil the shape of the plugs. Burnishing with 
the back of a knife is good. In inserting the plugs a slight twist 
should be given. Never touch the metal part of a plug with the 
fingers. In putting in or taking out a plug, be careful not to 
disturb the ones next to it. A plug from one box should not be 
used in another unless it has the same taper. A well-arranged 
bridge box will answer for the measurement of resistances from 
1/100 ohm up to 1,000,000 ohms. A larger size with 10,000-ohm 
coils may extend over a range of 1/1000 ohm to 10 meg-ohms 
(10,000,000 ohms). Thicknesses of the wire for the different coils 
are given thus: 

Coils of 1 ohm No. 18 to 21 B.W.G. 

Coils of 10 ohms No. 20 to 29 B.W.G. 

Coils of 100 ohms No. 25 to 34 B.W.G. 

Coils of 1000 ohms No. 32 to 40 B.W.G. 

A high-class resistance box or Wheatstone bridge box can have 
its top lifted off and turned upside down for inspection of the 



&32 



ELEUTRICIANSS' HANDY BOOK. 



coils, which are attached to the top and are lifted with it. A 
damaged coil can be removed and another put in its place, thus 
avoiding the necessity of sending the entire box to the makers. 

Wheatstone Bridge or Bridge Box.— This is a resistance box 
with its coils so arranged that the connections of the Wheat- 
stone bridge may be carried out with it. It has four binding posts 
for the end and galvanometer connections. It has already been 
shown in Fig. 479. 




Fig. 483.— Diagram of Wheatstone Bridge. 



The Wheatstone Bridge is an apparatus for determining the 
resistance of a conductor. 

If a conductor carrying a current is divided into two parallel 
conductors for a portion of its length, the following law will 
always exist: For every point on one of the parallel conductors 
there will always be a corresponding one on the other, between 
which, if they are electrically connected, no current will pass. 

Let the Wheatstone bridge be represented by a diamond. Fig. 
482, with opposite points connected. Let the four arms of the 



ELECTRICAL MEASURING IN8TRU3IENTS. 



633 



bridge be designated by a, h, c, and d. If no current flows through 
the wire indicated by g, the proportions will hold: 
a : h :: c : d and a : c :: b : d. 

In a proportion if three of the quantities are known, the fourth 
one can always be found by the arithmetical "rule of three." If 
therefore any three of the resistances are known, and if no cur- 
rent passes through g, the fourth or unknown resistance can be 
calculated by the rule of three. 

Suppose that an unknown resistance is to be determined. It 




Fig. 483.— SiMPiiB Whua^tstone Bridge. 



is placed in the bridge connection, at d it may be; theoretically, 
the place is indifferent. The current goes through it, and it must 
constitute the entire resistance of the arm d. Known resistances 
are put in for a and &. Suppose they are a = 100 ohms and & = 
5 ohms. Then one resistance after another is tried at c until no 
current passes through g. Suppose that this was 57 ohms. We 
then have the proportions: 

100 : 5 : : 57 : a^ or 100 : 57 ? : 5 : a; 
from either of which we find that 

X =: 2.85 ohms. 
This is the law of the Wheatstone bridge The apparatus is on^ 
of the most used in electrical work. To asce^rtiiiai when no our- 



634 ELECTRICIANS' HANDY BOOK. 

rent passes through g, a sensitive galvanoscope may be used. It 
need not be a galvanometer, that is to say, it need not be a meas- 
urer of current; it is enougli if it shows the presence of a current. 
It must be sensitive, as the slightest current must be shown by 
it if it exists. 

Fig. 483 gives a perspective view of a simple bridge to demon- 
strate the principle. 

Operation of the Wheatstone Bridge. — It may be operated on 
two principles. One of the resistances only may be changed until 
no current passes through the galvanometer connection, or two 
of the connections may be changed simultaneously, one being 
increased as the other is diminished. The latter method is used 
in a form called the meter bridge originally, but since its first use 
modified in various ways, so that it is no longer a meter bridge. 
The name meter indicated that two of the limbs, a and b for in- 
stance, are one meter in length when taken together, being rep- 
resented by a single straight wire. 

Another thing to be noted is that it is only necessary to know 
the value of one of the three resistances. If the proportional 
value of the other two to each other is known, it is sufficient. 

What is known as a Wheatstone bridge is usually a box filled 
with resistance coils and with connection points or binding posts 
representing the points of the diamond. If the cut. Fig. 479 
representing the horizontal plan of a bridge, be examined, it will 
be seen that the points of connection of the wires from the bat- 
tery represent the ends of the diamond. The galvanoscope is con- 
nected to points representing the top and bottom of the diamond. 
The loose wire running from the right-hand binding post, where 
the galvanometer is connected to the battery connection, is the 
wire whose resistance is to be measured. By putting in and 
taking out plugs, the relations of the resistances can be varied 
until the galvanoscope reads zero. 

Null flethod.— One great advantage about the bridge method 
is that the galvanoscope reads zero always when the resistance 
is determined. A calibrated instrument is not needed. It is 
what is called a null method. 

The rieter Bridge has been used for the most delicate re- 
searches. The cut, Fig. 484, shows the connections. The character- 



ELECTRICAL MEASURING INSTRUMENTS. 



635 



istie part from which it takes its name is the wire in this in- 
strument stretched three times along its front. This wire repre- 
sents two of the arms of the bridge. A sliding piece K moves 
along it, and by depressing a key connects the conductor from 
the galvanometer to the wire. This point represents the top or 
bottom of the diamond. The position of the point read off on 
the scale gives the ratio of resistance of the two sides represented 
by the stretched wire. By using one or the other of the three 
leads of the stretched wire, or by using two or three of them 




Fig. 484.— Meter Bridge. 



simultaneously, all sorts of proportions between the parts to 
right and left of R can be brought about. The known and un- 
known resistance represent the other legs of the diamond, and 
the point where tha other conductor from the galvanoscope is 
connected is the end of the diamond. The small figure shows the 
contact piece which is moved along the wire. 

Bridge Key. — In using the bridge, the current is only turned 
on momentarily for each trial adjustment, until the zero reading 
is reached. This would set the galvanoscope swinging, owing 
to the capacity of the elements of the bridge or of the conductor 
or to the capacity or inductance of the unknown resistance. A 



63& ELECTRICIANS' HANDY BOOK. 

key is used which makes two contacts in succession. The first 
connects the battery with the bridge circuits, and the second 
brings the galvanoscope into its circuit. Thus in the cut, Fig. 
482, when A is depressed, it first makes contact with B, thus 
bringing the battery and the four arms of the bridge on closed 
circuit. This instantly charges all parts and expends any induct- 
ance. A further depression of the key brings A, B, and C in con- 
tact, which operates to throw the galvanoscope into its proper 
circuit across the diamond. Two separate keys may be connected, 
so as to effect the same result. 

Shunt to the Galvanoscope. — This is sometimes used to di- 
minish its sensibility for the first trials. As the work approaches 
its finish, the shunt key is opened, allowing the galvanoscope to 
operate with its full degree of sensitiveness. In the cut. Fig. 482, 
the shunt is indicated by s and the shunt key by 7c, 

Proportional Coils. — This term is applied to the arms of the 
bridge opposite to the unknown resistance and the arm in series 
with it. Thus in Fig. 482 if c or (Z represents the unknown re- 
sistance, a and & are the proportional coils, 

Galvanoscope. — Although this term has been used, the gal- 
vanoscope actually employed is a galvanometer in most cases, and 
a highly sensitive refiecting instrument is adopted for delicate 
work. As a galvanoscope the telephone receiver is sometimes 
employed. 

Conditions of Sensitiveness.— The galvanometer must be sensi- 
tive. On inspecting the diagram. Fig. 482, on page 632, it will 
be seen that the battery and galvanometer can be interchanged. 
The one which has highest resistance should be placed so as to 
connect the junction of the two arms of highest resistance with 
the junction of the tw^o arms of least resistance. Thus, if the 
resistances are a = 1 ohm, 7; = 100 ohms, c = 4 ohms, and d 
= 400 ohms, the higher resistance apparatus or appliance, whether 
it is battery or galvanometer, should connect the junction of 
a and c with that of 7) and cl. The galvanometer will almost al- 
ways have the higher resistance. With galvanometers equal in 
all other respects except in the thickness and length of wire 
winding, the resistance for greatest sensitiveness will be ex- 
pressed by the following expression, referring to Fig. 482: 



ELECTRICAL MEASURING INSTRUMENTS. 



637 



(a + &) (c + d) 

a + h -\- G + d 
This is not a practical consideration, as the galvanometer cannot 
be changed for every new testing. 

Direction of Deflection.— The galvanometer will deflect one 
way for one change of relative resistances and the reverse way for 
the other change. This will hold only for the identical battery 
connections. It is recommended by some to mark upon the work 
table some indication for these deflections. Then by noting 
whether it is to left or right, the operator will know whether to 
increase or diminish the given resistance. Ordinarily, it will be 




Fig. 485.— Principle of the Potentiometer. 



one resistance that will be varied. The others will be plugged 
in and left untouched, perhaps for a number of tests. 

The Potentiometer is an apparatus for measurement of resist- 
ances, current strengths, and potential differences. It has ac- 
quired in late years most extensive application. Modern electric 
measurement practice tends or should tend in the direction of 
null methods. The potentiometer uses one of these. A reflecting 
galvanometer may be and generally is used with the potentiom- 
eter. Its function is simply as a galvanoscope, just as in the 
Wheatstone bridge method. When it shows no potential differ- 
ence, the reading of the resistance coils gives the result of the 
experiment. 

Principle of the Potentiometer. — In Pig. 485 W is a battery 



638 



ELECTRICIANS' HANDY BOOK. 



giving a constant current, R is an adjustable resistance, A B is a 
resistance divided into 150,000 parts, and by movable contacts 
M M' different lengths of it may be thrown into parallel with 
the circuit containing the galvanometer G and at B' a battery, 
not shown in place, because various cells are used there, E indi- 
cating the binding posts for connecting them. For general re- 
quirements the drop between M and M' must be at least 1.5 volts 
under the action of the main battery W, which is not a standard 
one. 




Fig. 486.— Potentiometer Connections* 



The standard cell is introduced at E, and the points E and E' 
are so set that the number of divisions of A B included between 
them represents the voltage of the standard cell. Suppose this 
voltage to be 1.434, then M and M' should include 1,434,000 di- 
visions of A B between them. The resistance at R is now varied 
until the galvanometer G shows a zero reading. For the stand- 
ard cell there is substituted a cell whose electromotive force is to 
be determined. The distance between M and M' is adjusted until 
the galvanometer again reads zero. The direct reading of the 
divisions gives the voltage of the cell. 

This merely gives the principle. In Fig. 486 is shown one of 
the developments. The galvanometer is seen at the bottom of 



ELECTRICAL MEASURING INSTRUMENTS. 



639 



the diagram. A double-throw switch throws it into circuit with 
the standard battery S or the battery to be tested, connected at E. 
The drop against which the standard cell S is balanced is the 
fixed resistance R s. By varying the resistance R, the zero read- 
ing of the galvanometer is secured with the connections shown 
in the diagram. The double-pole switch is then thrown to the 
right and M M' adjusted until a zero reading is obtained. The 
divisions of A B included between M and M' give directly the volt- 
age of the cell at E. R s is chosen of such resistance as to secure 
this relation. 




Fig. 487.— Potentiometer Connections. 



Another development is shown in Fig. 487, which approaches 
more closely than the last to the conditions of Fig. 485. The 
standard cell connects at fixed points on A B distant a number 
of divisions expressing as before its voltage. The cell to be 
tested is connected by a right-hand movement of the switch, and 
its voltage is determined as before for M M'. 

High=Voltage Determinations with the Potentiometer.— If 
the voltage to be determined exceeds that of the standard cell con- 
siderably, resistance is put in series with the cell to be tested. 
Connections to E are taken from known divisions of the resistance. 
Thus, suppose a 30-volt battery were to be measured, which is 



640 



ELECTRICIANS' HANDY BOOK. 



twenty times the capacity of the instrument. The battery would 
be connected through a resistance which might be 1,000 ohms. 
Taps from portions of the 1000-ohm resistance, including 50 
ohms between them, would be connected to B. The reading be- 
tween M and M' multiplied by 20 would give the voltage of the 
battery. 

In Fig. 487a the source of electromotive force which is to be 
measured is connected at E. M. F. By means of the switch N 
different portions of the resistance Q Q' can be connected to the 
potentiometer at P. For a high electromotive force the fraction 
E Q' of the resistance could be connected, giving a fraction of 



-O E.M.F. O- 



C D E 

Q 0\/WWWWWWVWWWWWVWVOVWVV' 



o 



Fig. 487a.— High- Volt age Connections for Potentiometer, 




the electromotive force expressed by the quotient of the entire 
resistance divided by the resistance E Q'. For less electro- 
motive forces the switch N is swung so as to connect with 
D or with C. 

Current Measurement with the Potentiometer. — The current 
is passed through a standard low resistance. The drop between 
its ends is determined by connecting branches from its ends at E. 
Knowing the drop and the resistance in which such drop occurs. 



the current is calculated by Ohm's law I 






To determine resistance by the potentiometer, the conductor 
under trial is put in series with a known resistance, and a bat- 
tery is connected in the circuit. The potential difference between 
the ends of the known resistance is determined, which depends on 



ELECTRICAL MEASURING INSTRUMENTS. 



641 



the current strength. The potential difference between the ends 
of the conductor under trial is next determined. As the current 
strength is supposed to be the same as before, the resistance of the 
conductor is determined by the relative drop. 
Should there be any apprehension that the current strength has 



— S7 




Fig. 488,— Resistance Determination by Potentiometer. 



changed between the two determinations, it is only necessary 
to make new- determinations, and if there is only a slight dif- 
ference the average may be taken. In order to secure a virtually 
constant current put good resistance in series with the battery 
and two working resistances. 

The connection is shown in Fig. 488. 



CHAPTER XXXVI. 

ELECTRICAL ENGINEERING MEASUREMENTS. 

Voltmeter fleasurement of Resistaace, — The following is a 
quick method of measurement v/ith simple appliances, A known 
resistance and voltmeter are all that are needed. 

Referring to the diagram. Fig. 489, D B is a source of current 
supposed to be constant during the time of the experiment, r is 
a known resistance, and R is an unknown resistance, which is to 
be determined. The voltmeter V is first placed across the ter- 
minals of one resistance, say of r, as siiov/n, and its deflection 
giving the drop or voltage is noted. It is then connected across 
the other resistance — in this case it would be the unknown one 
R — and its deflection also noted. Suppose that for R the deflection 

is E, and for r is e. We then have E : e : : R : r. or R = _?1^ 

e 
Voltmeter and Ammeter Determination of Resistance.— Sup- 
pose that we have a voltmeter and an ammeter, but no known 
resistance. Then we place the ammeter in circuit with the un- 
known resistance, and then connect the voltmeter across the ter- 
minals of the unknown resistance. The diagram. Fig. 490, shows 
the connections. E is the source of current, A is the ammeter. 
V is the voltmeter, and R is the unknown resistance. By Ohm's 

F 

law we have R == zi. The ammeter reading gives I, the voltmeter 

reading gives E; the quotient of E divided by I gives the resist- 
ance of the conductor R in the diagram. 

Low = Resistance Measurements. — With a milli-voltmeter low 
resistances can be measured by the above method. The diagram, 
Fig. 491, shows it applied to measuring the resistance of the ar- 
mature of a dynamo or motor. 

The terminals from the circuit containing the source of cur- 

643 



ELECTRICAL ENGINEERING MEASUREMENTS. 643 

rent E and ammeter A are connected to opposite bars of the com- 
mutator through the brushes, or directly by being pushed under 
the brushes between them and the commutator bars. With the 
milli-voltmeter m V connected as shown, the resistance of the 
armature can be measured, using the formula given in the last 
example. 

High=Resistance Measurements. — For high-resistance measure- 
ments the plain voltmeter may be used. Its resistance must be 
known, and figures as the known resistance r. The diagram, 





Fig. 489.— Voltmeter Determina 
TioN OF Resistance. 



Fig. 490.— Voltmeter and Ammeter 
Determination op Resistance. 



Fig. 492, shows the arrangement of the apparatus. E is the 
source of current, R is the unknown resistance, V is the volt- 
meter of the resistance r, and K is a switch. The voltage E 
through r is given when the switch is closed; the voltage E' 
through R + ^ in series when the switch is open. B is greater 
than B'. The unknown resistance R is given by the formula 

E — E' 



il. 



Line Insulation Tests. — 'The above method as applied to an 
active high-potential line to determine its insulation, is shown in 



644 



ELECTRICIANS' HANDY BOOK. 



Figs. 493 and 494. It is used to detect a ground. The voltmeter 
is connected with one terminal grounded first to one lead and 




Fig. 491.— Determination of Low 

Resistance with Voltmeter 

AND Ammeter. 







Fig. 493.— Voltmeter Measure- 
ment OF High Resist- 
ance. 



then to the other line. If the line is dead, a battery can be put in 
circuit with the voltmeter. Let E be the difference in potential 
between the lines, and E' the difference in potential between one 





Figs. 493 and 494.— Line TttstttjAtton Tests. 



line and the ground. Then calling R the line insulation and 

the known resistance of the voltmeter, we have: 

E — E' 
R = r — — — - 
E' 

Rail = Joint Test.— The resistance of rail joints is an impor- 



ELECTRICAL ENGINEERING MEASUREMENTS. 645 

tant factor in electric railroad practice. With a sensitive gal- 
vanoscope, such as a milli-voltmeter, reflecting galvanometer, or 
telephone receiver, it can be determined thus: 

Wires are secured to the rail just over the ends of the bond, 
or within a short distance of the joint and inside the limits of 
the bond. They are connected to the galvanoscope as shown in 
Fig. 495. The rail joint represents one arm of a Wheatstone 
bridge, the wire A B represents another arm, and the cross con- 
nection is made up of the galvanoscope and the two wires con- 
nected with it. From the point B another wire is taken, and is 
moved along the rail on the other side of the joint until nc 




Fig. 495.— Rail Joint Test. 



sign of current can be discerned in the galvanoscope. By the 
principle of the Wheatstone bridge the resistance of the joint is 
equal to that of the portion C D of the rail. Twelve inches is a 
usual distance for the space including the joint. The current 
passing in the rail from the operation of the road is the current 
which is used in the experiment. It may be necessary to protect 
the galvanoscope by resistances. If so, they must be placed as 
shown. A couple of keys as indicated are convenient also. The 

resistance of the joint is expressed as —^^ . This gives the length 

AD 
of rail equal in resistance to a joint. 
fleasurement of Insulation Leakage. — ^An insulated electric 



64© ELECTRICIANS' HANDY BOOK. 

cable represents a condenser or Leyden jar. The insulation is the 
dielectric, or a part of it. If the cable is an aerial one, the air is 
also part. If the cable is sheathed, the metal sheathing repre- 
sents the outer coating. Otherwise the earth or moisture on the 
cable may be representative of the outer coating. The inclosed 
conductor represents the inner coating. It can be charged just 
like any condenser. A definite quantity of coulombs or micro- 
coulombs of electricity at a definite potential can be charged upon 
the metal surface of its conductor if both ends are disconnected 
from everything, leaving the conductor insulated. If so charged 
and left to itself, the charge will slowly leak out, owing to im- 
perfect insulation. The resistance of the insulation determines 
the time. The value of the insulation in megohms, R meg., per 
mile is given by the following formula. In it C is the capacity 
in microfarads per mile of the cable, E the potential of charge at 
the beginning of a certain number of seconds T, and e the poten- 
tial at the expiration of that period. Then the resistance is given 
by 

26.06 
II meg. =__ 

Clog-? 
e 

Insulation leakage varies with this resistance, which is called 
the insulation resistance. 

Insulation Resistance of a Metal -Sheathed Cable. — This is 
the resistance between the wires and the sheath in a given length 
of cable. If it contains a quantity of wires, they are bunched at 
one end for the test, or for special purposes the wires may be 
tested individually. The diagram, Fig. 496, gives the theory of 
the connections. One wire is connected to the sheathing of the 
cable, one is connected to the bunched end of the wires; a special 
switch V is in parallel with the galvanometer G and shunt S. 
Thus the connections are the same as in a Wheatstone bridge, 
with the exception that the switch has been introduced, and 
that the insulation between wires and sheath in the cable takes 
the place of the unknown resistance of the bridge. A battery B 
and known resistances O and R complete the system. 

Before closing the circuit by connecting the wire to the cable 



ELECTRICAL ENGINEERING MEASUREMENTS. 647 

sheath or bunch of wires, the switch K is closed. Then the con- 
nections are completed, and the battery charges the cable. This 
sudden rush of current does not affect the galvanometer, as it goes 
almost entirely through the switch. The switch is now opened, 
and the galvanometer deflection, after it has stood a few minutes, 
is noted. To keep the deflections within proper limits, the shunt 
S may have to be adjusted. The battery must give the voltage 
used in determining the constant. 

If the same shunt has been used as was employed in deter- 
mining the constant, the galvanometer constant divided by the 




B== 



Fig. 496.~Insulation Resistance op a Metai>Sheathed Cable. 



deflection gives the meg-ohms resistance of the insulation of the 
cable tested. If a different shunt has been employed, multiply the 
result by the multiplying value of the original shunt and divide 
by the multiplying value of the shunt used in the test. 

The first deflection of the galvanometer is not noted. An extra 
quantity of electricity flows into the cable at first. After stand- 
ing a minute the reading is generally assumed to he correct. The 
slow absorption of electricity is termed electrification. 

Suppose that with a galvanometer shunt of g/999, the constant 
of 25,000 was determined, and that using the same constant and of 
course the sanie voltage on a cable insulation, the galvanometer 
Reflection was too small to be accurately read. Suppose the gal- 



648 



ELECTRICIANS' HANDY BOOK. 



of 55 resulted. The' insulation resistance would be 



vanometer shunt had to be changed to g/9d and that a deflection 

2500 1000 _ 
65 ^ 100 ^ 
454.6 meg-ohms. 

What is wanted is often the meg-ohms of insulation resistance 

per mile. In such case the meg-ohms found are multiplied by 

5,280 and divided by the length in feet of the piece of cable tested. 

Telephone cables show from 1,500 to 2,500 meg-ohms per mile. 

Determination of Capacity of a Cable.— When the capacity 




-i'l'l'l' ^ 

B 

Fig. 497.— Capacity Test. 




Fig. 498.— Determination or Capacity of a 
Cable. 



of a cable is to be determined, the ballistic galvanometer is used, 
and a standard condenser. A galvanometer shunt will ordinarily 
be needed unless the standard condenser and line to be tested have 
capacities rather close together. 

The cut, Fig. 497, shows the determination of the throw due to a 
standard capacity, which for telephone cables would be about 1/10 
microfarad. Seven or eight cells of battery may be used. C is 
the standard condenser, B the battery, G the ballistic galvanom- 
eter. On depressing the key the condenser is charged; 15 or 
20 seconds may be allowed for this. Then the key is suddenly re- 
leased, and it springs upward and connects the galvanometer to 
the terminals of the condenser. The latter discharges its charge 



ELECTRICAL ENGINEERING MEASUREMENTS. 649 

through the galvanometer, and the deflection, which is an in- 
stantaneous throw only, is noted. Next for the terminals of the 
condenser are substituted connections to the wire in a cable and 
to the outer metallic sheathing of the same. The distant ends of 
the wires are disconnected from the sheath and from the ground. 
The operations are repeated, and the throw of the galvanometer 
is again noted. The throw due to the discharge of the cable is 
divided by that due to the discharge of the condenser, and the 
quotient .is multiplied by the capacity of the condenser. The re- 
sult is the capacity of the cable. 

The connections for a capacity-testing apparatus are shown 
in the cut, Fig. 498. G is the galvanometer, S its shunt, C the 
standard condenser, V a double-pole switch, K K discharging 
switches, and B the battery. 

The switches K K are depressed on their lower connections. 
This brings the battery in circuit with the condenser. The 
latter should be arranged so that various capacities can be ob- 
tained from it. The battery now is allowed to charge the con- 
denser for 15 or 20 seconds, when the keys K K are released and 
the throw of the galvanometer is noted. The double-pole switch 
V is now thrown to the right. This substitutes the cable to be 
tested for the condenser. The switches K K are again depressed 
for 15 or 20 seconds and suddenly released, and the throw of the 
galvanometer again noted. 

If the shunt had to be used, the multiplying power used for the 
cable is divided by that used for the condenser, and the figure 
obtained as described on page 648 is multiplied by this quotient 
to get the capacity of the cable. 

The capacity of a cable affects its use in telephony; the greater 
its capacty, the more poorly will it work. An interesting appli- 
cation of the test is involved in the determination of a break in 
the conductor of a cable. It is only applicable in cases where 
there is high insulation resistance — a meg-ohm at least. 

The capacity of the broken wire or conductor is determined 
first from one end of the cable, and then from the other end. It 
is perfectly evident that the capacities of the two parts will vary 
as their lengths. A simple proportion will give the lengths. 

Thus, call X the distance to the break from one end, and K the 



650 ELECTRICIANS' HANDY BOOK. 

capacity of this part, K' the capacity of the other part, and a — x 
the distance to the break from the other end. Then we have the 
proportion: 

K : K' :: X : a — x . 

K'£i7 = Ka — K X 

(W + K) x — Ka 

K a 

X =-- 



K + K 

If there is a good wire in the cable, this can be used to avoid 
the necessity of carrying the instruments from end to end of the 
line. Deflections are obtained, d for the near section of broken 
wire, d' for the good wire, and d" for the good wire connected 
to the distant broken section, which last gives the sum of the 
deflections due to the good wire's and distant section's capacities. 
Hence the capacity of the two sections of broken wire is d" — 
d' + d. As before let x be the length of the near section and a 
the total length of the wire. Then the deflections being propor- 
tional to the capacities, and consequently to the lengths of the 
wires, we have: 

d'' — d' -]- ~n : d :: a : X 
a d 

~~ d" — d'-\-d 
If there is low insulation resistance, this test is inapplicable. 
If the capacity of the cable per mile or other unit of length is 
known, a determination of the capacity of the near section gives 
the requisite datum in combination with what is known to calcu- 
late the location of the break. Thus, call the capacity of a mile 
of submarine cable K, and that of the broken section K'. It is 

rr 

evident that the length of this section is equal to — -. As before, 

K' 

the deflections may give it directly if those due to capacity K are 
known. As K' might be due to many miles or only a few, the 
galvanometer shunt might have to be used, and possibly different 
galvanometers for extreme cases. This would introduce simple 
multiplication factors or divisors into the calculation. 

Galvanoscope Cable and Line Tests. — An uncalibrated gal- 
vanometer with three or four cells of battery is useful for testing 



ELECTRICAL ENGINEERING 3IEASUREMENTS. 651 

lines for grounds, crosses, or breaks. One terminal of the battery- 
is grounded, the other end is connected to the end of the line 
to be tested, which must be on open circuit at the near end. The 
galvanoscope will be apt to move at the instant the connection is 
made. Suppose that the distant end of the line is on open circuit 
also. A permanent deflection of the galvanoscope will indicate 
a ground. Suppose there is no deflection. Then as the line has 
shown no ground, the distant end is to be next connected to earth. 
If the galvanoscope shows a permanent deflection, the line is con- 
tinuous and without ground. But if the galvanoscope shows no 
deflection on the second test, the line is broken somewhere, and 
the part beyond the break may be full of grounds. The break 
prevented them showing on the first test. 

If on the first test the galvanometer gives a strong throw of 
the needle, followed by a return to zero, it goes to prove that the 
line is continuous, as this throw is due to the capacity of the 
line, and the capacity is greater as the line is longer. But there is 
nothing accurate about this test. If the observer knows the line 
and knows the instrument, he may draw a useful conclusion from 
the observation of the first throw of the needle. Such conclu- 
sions are on a par with those which an observer draws from the 
loudness of the ring of his magneto bell. 

With a galvanometer and battery, all the wires in a cable can 
be rapidly tested for crosses, by connecting across from one to 
another seriatim or in succession. Thus one wire can be con- 
nected through the galvanometer and battery to all the others 
bunched. The distant ends of the wires in the cable are supposed 
to be disconnected or on open circuit. If no permanent deflection 
is shown, one wire is shown to be all right, and without cross 
connection with any of the others. This wire is bent aside, tagged 
or marked if desired, and the end of another wire pulled out of 
the bunched ends, and is tested against the rest of the wires. 
This time there is one less wire in the bunch than before. If the 
wire is without cross, it is put aside and another tested. Eventu- 
ally, only a pair will be left to be tried, one against the other, 
if no crosses have been found. A cable full of wires can be 
rapidly gone through. If a ground is found, it will be between 
the single wire and one or more of those left in the Mnch. By 



652 



ELECTRICIANS^' HANDY BOOK. 



testing one wire after another out of the bunch against the crossed 
wire, the fault can be located as far as the specific wires are con- 
cerned. The two or more wires which are crossed can be found 
and tagged or marked, so as to exclude them from the working 
wires of the cable. 

Frequently the testing is done to cables while rolled up on the 
wooden reels on which they are transported. The cable on a 
reel is tested and found perfect, and is then drawn into the duct 
in the conduit. Wires found defective should be tagged with the 
indication of their defect, whether grounded, crossed, or broken. 




Fig. 499.— Cable Testing on Keel for Breaks in Wires. 

Cables are supposed to be subjected to severe tests by the manu- 
facturers, so that new cables are often assumed to be perfect, 
and no test is applied by the purchasing company. There are 
two possibilities. One is that the cable has been injured in trans- 
portation; the other is that it may be injured in being drawn into 
the duct. 

Tests of Cable on Reels.— When cables are still on reels, both 
ends are accessible, and they can be conveniently tested. The 
cut, Fig. 499, shows the connection for finding breaks of contin- 
uity in individual wires of a cable. The bunched ends of the 
wires at one end are connected to a battery and galvanoscope. 
The other end of the wire of the circuit is touched to the other 
ends of the cable wires, one by one. These ends are opened so as 



mk 



ELECTRICAL ENGINEERING MEASUREMENT,"^. 653 

not to touch each other. As shown in the cut, a bell is used as 
galvanoscope. A ringing will indicate that there is no break in 
the wire which is touched. The test for crosses should also be 
made. 

Finding Wire Ends in a Cable. — It will be seen that similar 
tests can be applied to picking out the two ends of a wire in a 
cable. The distant end of the wire is grounded. The near end 
of one wire after another is connected through the battery and 
galvanometer to the ground, until the galvanometer shows the 
existence of a current. 

Making Brancti Connection In a Cable. — Sometimes it is de- 
sired to take a branch line from an intermediate point in a cable. 
The above test can be applied to pick out a wire from the cable 
whose sheathing has to be opened for the purpose of making the 
connection. The distant end of a wire is grounded. The wires 
are loosened or opened. Connection of one wire after another is 
made with the galvanometer and battery which are grounded. 
The connection is made by means of a pointed wire or needle 
point, which forms the terminal of the wire from the battery 
and galvanoscope. This is thrust through the insulation of one 
wire after another in the opened part of the cable, until the indi- 
cations of a current on the galvanoscope show that the right wire 
has been found. 

Tiie Telephone as a Galvanoscope. — The telephone, whose 
diaphragm gives a sharp click upon making or breaking an active 
circuit of which it forms a part, is an exceedingly sensitive indi- 
cator of current. It can be substituted in many cases for a 
galvanometer, being connected in series with three or four cells 
of dry battery. Portable sets are made for this purpose, com- 
prising a pocket battery and small telephone. Where much testing 
is to be done, a strap or spring should be used to hold the tele- 
phone against the ear of the observer. Otherwise, where perhaps 
a hundred wires in a cable have to be tested, the work of holding 
the telephone by hand will become quite laborious. The tele- 
phone and battery represent the combination of hand magneto 
and bell. The test is made by touching and separating the end 
of a wire in the circuit to the telephone terminal, or by otherwise 
suddenly making and breaking the current. Due regard must 



654 



ELECTRICIAN,'^' HANDY BOOK. 



he had to capacity of the wire. A click in the telephone will be 
produced by this alone if it is at all considerable. 

The following method of using the telephone test for crosses 
and grounds in a cable is given in Roebling's pamphlet on tele- 
phone cables. It may be applied most conveniently to cable on 
the reel, as both ends are then accessible from the observer's posi- 
tion. At the near end of the cable the wires are spread a little, 
and the particular wire under test has a short piece of wire con- 
nected to it. The rest of the wires are bunched, and by a short 
piece of bare wire are connected to the sheath of the cable. The 
arrangement and connections are shown in Fig, 500, 




Fig. 500.— Cable Testing on Eeel for Short Circuits. 



By a short piece of wire one terminal of the battery is con- 
nected to the cable sheath. The other terminal of the battery is 
connected with the telephone. The observer holds in his hand 
the end of the wire, which is connected to the wire to be tested. 
He suddenly taps with it one of the binding posts of the tele- 
phone. This gives it a charge of electricity, and if it is not 
crossed or grounded, which means connected to the lead sheath 
of the cable, a click will be heard in the telephone. This 
tells nothing. But if the wire is in good condition as regards 
crossing and grounding, it will hold its charge, and on a sec- 
ond tap being given the telephone will give no sound or a great- 
ly diminished one, and a third tap will be almost sure to produce 
no sound whatever. But if the wire is crossed or grounded, a 



I 



ELECTRICAL ENGINEERING MEASUREMENTS. 655 

closed circuit will result from each tap. The circuit will include 
the telephone, battery, sheath, and wire, and perhaps another 
wire or wires if there is a cross; consequently, in such a case 
every tap will give a click on the telephone. 

If no click is given on the first tap of all, it will indicate that 
the wire is broken off, probably close to the observer. 

Even moisture in the cable will impair the insulation enough to 
give the indications described. The loudness of the click will give 
some clew to the extent or degre-e of the trouble. 

It will be seen that the test for continuity of the wire is a part 
of the test for crossing and grounding. The telephone can be 




BAD WIRE X ^ Y 



GOOD WIRE Q 



FAULT 



Fig. 501.— Varley's Loop Test. 



used for it. A continuous clicking, as the telephone terminal is 
tapped, represents a permanent deflection of the needle of the gal- 
vanoscope. 

The Vibrating Magneto Bell as a Galvanometer. — A vibrating 
bell can be used in tests where a galvanometer is applicable. 
Three or four cells in series with it give the current. It is very 
convenient for continuity tests. 

Some of the tests just given are not quantitative — ^which means 
that no measurement of current, resistance, or other function is 
executed. An idea of the degree of trouble with a cable can be 
obtained from the indications of the instruments, but that is all. 
Experience will teach the observer to place the right amount of 
dependence, rather little than much, upon differences of degree 
■which have been alluded to, 



656 ELECTRICIANS' HANDY BOOK. 

Varley Loop Test. — This is an application of the Wheatstone 
bridge. Suppose that there is a bad wire in a line, as shown in 
Fig. 501. Its distant end is connected to the end of a good wire, 
and the two are connected into a Wheatstone bridge, as shown. 
The battery is grounded as shown; the points i and e represent 
the ends of the bridge, R + X is the resistance of one arm of the 
bridge; C + Y is that of the other. We have as the equation of 
the bridge: 

A R -l-X 
B ~ C + Y 
The entire resistance of the two wires is equal to X + Y + C. 
Calling this resistance L, we have: 

L = X + C + YandL — X=:=C + Y. 
Substituting L — X for C + Y in the first equation, we have: 

A_?_±ZandX= -^L-BR 
B~L-X A+B 

If the resistance A is eaual to B, we have: 
IT L-R 

If L is known, X can be determined; L. is found by calculation 
from the size and length of the wires or from records. If there 
is only one ground, it can be measured by bridge connection, the 
battery terminal being taken from the ground and connected 
between R and X. 

Hand flagneto Tests.— The hand magneto is a bipolar gener- 
ator with shuttle or H-section armature. The latter is rotated 
by multiplying gear, and the current is taken off by two contact 
rings. 

It is made in stock size, and is in itself a rough measuring in- 
strument. A bell is mounted in the box, whose armature is 
polarized and is acted on by an electro-magnet. The winding 
of the magnet is in circuit with the armature winding of the 
magneto. On turning the handle, the bell will ring if its circuit 
is closed. The diagram. Fig. 502, shows the connections. 

The hand magneto is much used in testing insulation. One 
terminal may be connected to a line to be tested, and the other 
terminal to a water or gas pipe to give a good ground. On 
turning the handle, the bell will ring if the insulation of the liuQ 



ELECTRICAL ENGINEERING MEASUREMENTS. 



657 



is defective within the limits of the sensitiveness of the instru- 
ment. The magneto in question with its bell is generally so 
wound that the bell will ring through 20,000 to 25,000 ohms. 

By practice and use of the same magneto, the operator using it 
can roughly approximate to the seriousness of a ground, or to the 
resistance of the circuit rung through, if he notes the loudness 
of the bell and the clearness of its ring. It is dangerous to rely 
too much on such indications. 

Hand Magneto Test for Ground — If a line or cable is to be 
tested for grounding, the circuit is opened at both ends. The 




Fig. 502.— Hand Magneto and Bell for Testing. 



practical point is to be sure that the far ends of the line wires 
are on open circuit. The near end is opened, connected to the 
magneto, and the other end of the magneto circuit is grounded. 
If the bell rings on turning the handle, the assumption is that 
there is a ground. 

But simple as this test seems, it is not reliable. The alternat- 
ing current produced by the magneto may, by charging and dis- 
charging an ungrounded line of some capacity, ring the bell and 
so lead to false conclusions. This test is of great use where the 
line is of slight capacity, which is the case with a bare wire on 
poles. But cables with metal sheathings represent a sort of 
Leyden jar, and may ring the bell when there is no ground upon 
them, 



65S ELECTRICIANS' HANDY BOOK. 

Hand Magneto Test for Cross Connections. — To test for a 

cross connection in a cable, one terminal of the magneto is con- 
nected to the wire to be tested, and the other to the ends of the 
remaining wires, which are bunched for the purpose. If the bell 
can be rung, a cross is present. The test can be applied if de- 
sired to a single pair of wires, so as to go thr/Dugh the cable wire 
by wire instead of bunching all except the one. 

Engineering Tests. — The distinction between engineering and 
laboratory tests and measurements is definite. Much apparatus 
is used in laboratory work which it would be quite impossible to 
employ in outdoor work in the streets of a city. Any tendency 
to the refinement of what may be called street tests is accomp- 
anied by a corresponding tendency to apply the finer processes 
of the laboratory to more and more of the every-day prohlems 
which confront the engineer. It is therefore a fair conclusion 
that the distinction between the two classes will always exist. 
The object of the engineer should be to use the finest class of 
measurements in his work, and to constantly appeal to the lab- 
oratory for final data. 



J 



CHAPTER XXXVII. 

ELECTROPLATING. 

Electroplating. — The decomposition of a metallic salt by the 
electric current in such a way that the metal is deposited where 
desired constitutes electroplating. To deposit metal, a current 
must pass through the solution by electrolytic conduction. This 
gives the general case without reference to electrons or to the 
ionic theory. The latter only affects the theory of the case. 

Energy Absorbed in Electroplating.— The rate of expenditure 
of electric energy is expressible in volt-amperes or watts. To 
deposit metal some current must pass through the solution, be- 
cause each coulomb precipitates a given and invariable amount 
of each metal. Until some current passes, no metal will be de- 
posited. If the current passing through a given bath be multi- 
plied by the voltage required to force the current through the 
bath, the rate of energy will be given in watts or volt-amperes. 
- The voltage may be derived from an outside source, such as a 
battery or dynamo, or part or all of it may be derived from the 
bath and its electrodes. A Daniell's cell is an example of a 
plating bath, which deposits copper upon a surface of copper, the 
reaction between the electrodes and solution producing all the 
required voltage. . If copper electrodes are immersed in a bath of 
copper sulphate and a current is passed through the solution, all 
the voltage is derived from an external source. In other cases 
the solution and electrodes may generate part of the voltage 
only, the rest being supplied from an external source. 

General Principles. — The general principle is easiest fixed on 
the mind by reference to the primary battery. If from the 
terminals of such a battery wires are led to a bath filled with a 
plating solution, and if the ends of the wires are attached to ob- 
jects of metal adapted for the purpose, and if the metal objects 



660 ELECTRICIANS' HANDY BOOK. 

are immersed in the bath, electro-deposition of the metal of the 
bath will take place, and the object connected to the zinc plate 
of the battery by the wire will have metal deposited upon it. 
The one attached to the copper, carbon, or platinum plate of the 
battery will have no metal deposited on it, and in many cases will 
be dissolved in the bath, and gradually disappear. 

Anodes.— The plate on which no metal is deposited is called 
the anode. Thus, for nickel-plating nickel anodes are a regular 
article of commerce. They are dissolved in the nickel bath in 
the course of the plating operation. For each ounce of nickel 
deposited, an ounce should be dissolved. There are other terms, 
such as cathode, for the plate on which metal is deposited, which 
have never come into general use. 

Reproduction. — Electroplating is used for two purposes. One 
is to reproduce objects. To do this, a mold is taken fronl the 
object. This mold may be of wax, papier mache, fusible metal, 
or any substance which can be made to give a reversed reproduc- 
tion of the object. A thick layer of metal may be directly electro- 
plated on the object. This layer peeled or stripped from the 
original gives a reversed reproduction. On such the metal is 
deposited, which on removal obviously gives the direct unre- 
versed reproduction of the original object. The other purpose is 
to coat one metal with another, as spoons and other table ware 
are coated with silver. 

Current for Electroplating.— A source of heavy current and of 
low voltage is required for electroplating. If a battery is used, 
it is a low-resistance battery. The amperes required are generally 
found by determining the area to be plated, and allowing a definite 
amperage to each square inch or other unitary area of the 
articles. A solution is contained in a vessel, which is called the 
bath. The objects to be plated are immersed in it, and opposite to 
them are the anodes. The wire from the zinc pole of the battery, 
if such is used, or from the corresponding pole of the dynamo, 
is connected to the objects. The other wire is connected to the 
anodes. As current passes, the metal is deposited. The voltage 
varies for different solutions. From one to ten volts is a good 
range. It must be noted that a high voltage does no harm as 
long as the current is of proper strength, but the voltage must 



ELECTROPLATING. 



661 



be high enough to produce the requisite current and to decom- 
pose the solution. 

Regulation of Current.— The strength of current is regulated 
by adjusting the resistance in the circuit. A simple resistance 
frame, such as is shown in Fig. 503, is often used for this pur- 
pose. As the handle is swung in the direction indicated by the 
arrow, it cuts in less resistance. 

Simple Plating Apparatus. — Electroplating on the small scale 
is often done by the amateur with 
apparatus on the lines of the Daniell 
battery. Fig. 504. The object to be 
electroplated or reproduced takes 
the place of the copper electrode, 
and is attached by a wire to the zinc 
electrode. If the object is of a 
metal electro-negative to zinc or is 
coated with plumbago, copper will be 
deposited on it. Fig. 505 shows a 
circle of porous cups in a circular 
tank containing zinc plates, all con- 
nected by a circle of wire. A metal 
cross rests on the circle, and carries 
at its center the object to be plated. 
The large tank contains copper 
sulphate; the porous cups, water 
with a little salt. 

Large Plating Apparatus. — The 
illustration. Fig. 506, shows a bath 

for electroplating, around whose upper edge two frames of 
metal run. The outer frame is a little higher than the other. 
Long rods rest upon the outer frame, and the anodes are sus- 
pended from them, and short wires rest on the inner frame. The 
objects to be plated are suspended from these wires. One frame 
is connected to one pole, the other to the other pole of the battery 
or other source of current. The next cut, Fig. 507, shows a plat- 
ing bath A and battery D . . . . There are two main wires or 
bus-bars, a h and c d. One has the anodes K K connected to it 
by transverse wires m m; the other has the objects connected 




Fig. 503.— Electboplateb's 
Resistance Frame. 



662 



ELECTRICIANS^' HANDY BOOK. 



to it. One battery pole is connected to one bus-bar, the other to 
the other. Insulation is applied to the wires where required to 
prevent short circuits. 

Metals Deposited. — Copper, nickel, silver, and gold are the 
metals generally deposited. 

CoppersPIating.— The bath, for objects not attacked by sulphuric 
acid or copper sulphate, may be a solution of copper sulphate 
with one-tenth of its volume of sulphuric acid. It should have a 
density of 1.197, and is used cold. If the bath contains too much 
copper sulphate, this will form crystals on the surface of the 





m 



Fig. 504.— Daniell's Battery 
Plating Apparatus. 



Fig. 505.— Large Daniell's Battery 
Plating Apparatus. 



anode. Such crystals, perhaps invisible, will prevent the passage 
of current. This bath is of limited application, as it cannot be 
used for iron or zinc. It is applicable to wax molds, such as are 
used in electrotyping. 

For depositing copper on zinc and similar metals, the following 
baths are applicable: Copper sulphate, 2 pounds; water, 1 gallon. 
Add ammonia until the precipitate first formed is just redissolved. 
This colors the solution blue. Then add potassium cyanide until 
the blue color disappears. This bath should be used at a tem- 
perature of 122° F. to 131° F. (50° C. to 55° C). 

If zinc is' to be plated, the piece is first dipped into a mixture of 
4.5 per cent sulphuric acid, and then after washing into a solution 



ELECTROPLATING. 



663 



of caustfc soda or of sodium carbonate. It is then ready for 
plating. 




Pig. 508.— Electroplater's Bath. 

Electroplating sucli metals as iron or zinc is only to be recom- 
mended for special purposes. On any water getting at the zinc 
or iron, galvanic action commences and the metal is attacked. 




Pig. 507.— Electroplating Apparatus. 



In Paris copper-plating has been applied to lamp-posts for the 
streets, they being first varnished, or coated with oil mixed with 
copper powder. It is not a perfect success. 



664 ELECTRICIANS' HANDY BOOK. 

One case in which iron may be copper-plated with advantage is 
when the metal is to be silver- or gold-plated, and a preliminary 
copper -plating is often recommended as a preparation for nickel- 
plating on iron. 

Copper and potassium tartrate and copper and ammonium oxa- 
late are bases of the formulas. 

Before copper-plating iron, it should be dipped in dilute sul- 
phuric acid, and then after washing into an alkaline solution, as 
prescribed for zinc. 

Nickel-plating.— The following are formulas for nickel-plating 
baths with sulphates as the base: 

Ammonium and nickel sulphate. . . 4 parts 1 part 

Distilled water 100 parts 10 parts 

Ammonium carbonate (about).... 3 parts 
The double sulphate as above is a salt very much used in 
nickel-plating. 

The chloride may also be a basis for nickel-plating as in the 
following formula: 

Nickel chloride . .■ 298 parts 

Water 2250 parts 

Dissolve and add 

Ammonium chloride 70 parts 

Water, enough to make 10,000 parts 

Edward Weston recommends the addition to nickel-plating 
baths of boric acid — 2 parts of boric acid to 5 parts of nickel 
chloride or 1 part of boric acid to 3 parts of nickel sulphate. 

Too much alkali in a nickel bath gives a yellow deposit; too 
much acid gives a non-adherent coat. The bath must be per- 
fectly neutral. The bath should have a specific gravity of 1.041 
to 1.056. If it is weaker, the bath works slowly; if stronger than 
specific gravity 1.070, salts crystallize on the anodes. The bath 
must be constantly watched for changes in its specific gravity. 

The pieces to be plated must first be polished, the last polishing 
being given with powdered lime. The pieces are cleaned of 
grease with a 10 per cent solution of caustic potash. They are 
sometimes scrubbed with a brush in a mixture of warm water, 
Spanish white, and sodium carbonate. Sometimes benzine is 
used to remove grease. 



ELECTBOPLATINa. 665 

If copper is to be nickel-plated, it is first dipped into a 10 per 
cent solution of nitric acid, and after washing is dipped into a 
solution of 5 parts of potassium cyanide in 100 parts of water. 

For iron the first acid dipping bath is a 1 per cent solution of 
sulphuric acid. The pieces are rubbed with powdered pumice 
stone, and then dipped in a 20 per cent solution of hydrochloric 
acid. Iron objects must at once be put into the bath after 
treatment; otherwise they will rust. A thin plating with copper 
may precede the nickel-plating. 

Zinc can be nickel-plated by receiving first a good coating of 
copper, or it may be amalgamated. The latter tends to make it 
almost as brittle as glass. 

On removal from the bath nickel-plated objects are first washed 
in cold then in hot water, and are dried in wood sawdust. They 
are polished by regular processes. 

Nickel anodes must be chemically pure; they are suspended 
by nickel wires. Their surface area must be a great deal larger 
than that of the objects to be plated, because the solutions dissolve 
nickel with difficulty. It is a great object to have the anode dis- 
solve exactly as fast as the metal is deposited. If this occurs, the 
solution remains of unvarying strength. 

The voltage to be used varies. It may start as high as 5 volts, 
and is to be reduced v/hen the piece appears white, and may 
eventually run down to 1 volt. The evolution of hydrogen must 
be kept down as much as possible, although there is always more 
or less of it. Change of relative position of the anodes and 
pieces to be plated is often advisable, to prevent the deposition 
concentrating itself on salient parts. 

Silver=Platmg.— Baths for silver-plating are generally made 
of potassium-silver cyanide. Pure silver nitrate is the starting 
point for this preparation. The following are examples of silver- 
ing solutions: 

A solution of silver nitrate in water is precipitated by addition 
of lime water, the silver oxide appearing as a brown powder. The 
precipitate is washed with care, and is kept in vessels full of 
water. To prepare a bath for plating, some of the brown oxide is 
dissolved in solution of potassium cyanide in distilled water. 

A solution of silver nitrate may be precipitated by solution of 



666 ELECTRICIANS' HANDY BOOK. 

potassium carbonate, or of sodium chloride (salt), and treated 
as above. 

332 parts of silver nitrate are precipitated by hydrocyanic 
acid. The acid must be made immediately before use by adding 
nitric acid to potassium cyanide in quantity just sufficient to 
neutralize it. The precipitate is washed and put into 10,000 parts 
of water, and dissolved by addition of potassium cyanide. 

One or two thousandths of ammonia added to a bath improves 
the adherent power and brilliancy of the deposit. A very small 
quantity of carbon disulphide is sometimes added for the purpose 
of securing a bright deposit. 

To obtain an even deposit, the pieces in the bath must be moved 
about. This is sometimes done mechanically. The anodes are 
of pure silver, and their surface should be about equal to that of 
the pieces to be silvered. Iron or lead wire is used to hang them 
by. Copper wire must not be used, as it would dissolve and in- 
jure the solution by introducing copper into it. 

At least 4 inches space must be between the anode and the 
pieces to be plated. On commencing, a current of 42 to 43 amperes 
per square yard of surface to be plated is required. A potential 
of not over 2 to 3 volts is also prescribed, although it is to be 
remembered that as long as the voltage is sufficient, the amperage 
is the critical thing in electroplating. After a quarter of an hour 
in the bath the pieces are taken out and examin-ed to see if they 
are acquiring a uniform coating. They are then washed in a 
warm solution of potassium cyanide and replaced in the bath, 
and left there until the plating is thick enough for the require- 
ments. Four hours should complete the operation if there is 
enough current. Every 3600 coulombs or each ampere-hour de- 
posits 62.4 grains of silver. 

"When the deposition is completed, the pieces are removed from 
the bath, washed with clean water, and then with water slightly 
acidulated with sulphuric acid. They are finally brushed and 
polished by the regular processes. 

Preparation for Silvering. — Preparation of articles to be silver- 
plated begins with the removal of grease by boiling for a few 
seconds in a ten per cent solution of caustic potash. This is fol- 
lowed by washing in water and then dipping in a ten per cent 



ELECTROPLATING. 66? 

solution of sulphuric acid and water and washing. Next they 

are passed through a bath composed of 

Nitric acid (36°) 100 parts 

Salt (sodium chloride) 2 parts 

Calcined lampblack 2 parts 

After a few seconds they are washed vigorously, and then are 

passed at once through this bath: 

Nitric acid (36°) 600 parts 

Sulphuric acM (66°) 80 parts 

Salt (sodium chloride) 4 parts 

Again they are vigorously washed and placed in the "quick- 

ing" bath until they appear white on the surface. This bath is 

made up of: 

Water 100 parts 

Mercuric nitrate 1 part 

With enough sulphuric acid to dissolve the mercuric nitrate. The 

pieces are then washed and put into the plating bath. 

Qold=Plating.— Gold-potassium cyanide is used for the bath. 

154 parts of gold chloride are dissolved in 2000 parts of water. 

A separate solution of 200 parts of potassium cyanide in 8000 

parts of water is made. The two solutions are mixed and boiled 

for half an hour. 

This bath is employed at the ordinary temperatures. To keep 

up its strength, gold chloride and potassium cyanide may be 

added in equal parts as needed. The anode is a plate of gold. A 

bath too rich in gold gives a blackish or reddish coating. A gray 

coating slowly formed indicates too much potassium cyanide. 

Platinum suspension wires are employed for the anode. The 

anode should not be left in the bath except during the plating. 
For gilding with a warm solution the following baths may be 

used: 

1. 2. 

Sodium phosphate (crystallized). 600 parts. 500 parts. 

Sodium bisulphite 100 parts. 125 parts. 

Potassium cyanide 10 parts. 5 parts. 

Gold chloride 12 parts. 12 parts. 

The first formula is for gold-plating silver, copper, and alloys 

rich in copper. The second formula is for iron and steel; 



668 ELECTRICIANS' HANDY BOOK. 

The sodium phosphate is dissolved by heat in 8000 parts of 
water, the gold chloride in 1000 parts of water, and the two 
solutions are mixed. The remaining salts are dissolved in 1000 
parts of water and added to the others. This gives nearly 10,000 
parts of solution by weight, or about a one-tenth of one per cent 
solution of gold cyanide. 

These baths are employed at temperatures of 122° to 176° F. 
(50° to 80° O- A few minutes is time enough to give a coat- 
ing. A platinum anode is used. If a large area is immersed, the 
deposit is reddish in color; if the anode is partly withdrawn, the 
tendency is toward a pale deposit. 

This bath is best made up new as required. Enriching it by 
addition of gold salt and potassium cyanide is not recommended. 

The reason so short a period of plating is required is that gold 
has the property of giving an exceedingly thin and uniform 
coating. A very small thickness "covers." 

PIatinum=Plating. — Platinum-plating is not often done. The 
following is a formula for the solution for plating copper and its 
alloys : 

Dissolve 17 parts platinic chloride in 500 parts of distilled 
water. Dissolve 100 parts ammonium phosphate in 500 parts 
of distilled water. Mix the solutions. A precipitate will be 
formed. Little by little a solution of 500 parts sodium phosphate 
in 1000 parts of water is added and the whole is brought to boil- 
ing, water lost by evaporation being constantly replaced until, 
the ammonia being boiled away, the solution becomes acid and 
loses the yellow color it possessed and becomes colorless. 

This bath is used hot with a strong current, and its strength 
must be kept up by additions of the ammonium-platinum phos- 
phate precipitate, obtained as above described. 

Another formula is carried out by adding to a solution of 
platinum chloride a sufficient excess of potassium cyanide to form 
a clear solution of ammonium-platinum cyanide. A moderate cur- 
rent is required, or else a black powder will be deposited. 

The anode in platinum-plating is always platinum. 

Tin.— The following is a solution for the deposition of tin: 

Sodium pyrophosphate 10 parts. 

Water 1000 parts. 



ELECTROPLATING. 669 

In this solution is dissolved 1 part of fused tin chloride (stan- 
nous chloride, tin protochloride). There is liable to be some 
difficulty in the solution. If pieces of the tin chloride fall to the 
bottom, they may become coated with a sort of crust which is 
difficultly soluble, and which retards the solution of the tin salt. 
One way is to put the tin salt into a perforated ladle, like a cul- 
lender, and keep the salt near the surface of the liquid, and agi- 
tate it until it dissolves. 

The anode is of tin. The strength of the bath is maintained 
by adding, by means of the perforated ladle, equal parts of sodium 
pyrophosphate and tin chloride. 

Another solution is made thus: Metallic tin is dissolved in 
hydrochloric acid, and is precipitated by addition of caustic potash 
solution. The precipitate is mixed with a solution of potassium 
cyanide and caustic potash until it dissolves. 

Steeling. — A coating of iron is sometimes deposited on copper 
electrotypes of engravings in order to harden the surface. The 
iron thus deposited is so hard and durable that it is sometimes 
termed steel, although it is not steel at all, but pure iron. The 
bath may be thus prepared: 

A solution of 1 part sal-ammoniac (ammonium chloride) in 5 
parts of water is made. In it are suspended two plates of iron 
connected to the poles of a strong battery. After some hours the 
solution is ready, as some of the iron will be dissolved. 

The electrotype which is to be steeled is put into the bath after 
thorough cleaning and washing with caustic potash solution. 
About 4 volts electromotive force are prescribed. After the 
steeling the plates are washed in cold water and rubbed with 
benzine. To preserve them from rusting they are covered with 
a film of beeswax. 

Size of Conductors. — The conductors leading from the source 
of current to the bath should be as thick as convenient. All re- 
sistance of battery, generator, and conductors absorbs energy, 
which is wasted. The slight additional expense of large conduc- 
tors is compensated for by the economy of power. 

Current Intensity. — The quality of the deposit is greatly modi- 
fied by the intensity of current per unit area of surface plated. 
Thus in a copper-plating bath too strong a current will give a 



670 ELECTRICIANS' HANDY BOOK. 

brown deposit almost powdery in quality. To remedy any sucli 
tendency when it is observed, the current strength must be dimin- 
ished. This is easily done by raising the anode so as to decrease 
its immersed surface. Another way is to move the anode and ob- 
jects plated away from each other in the bath. 

If the current is too weak, the anode can be dipped deeper, or an 
extra one added, or the distance spoken of above can be de- 
creased. The latter is only advisable when a rather flat surface is 
being plated, because an irregular piece near the anode will have 
a thicker deposit formed on its protuberant parts than on its 
retreating parts. The difference in distance between projections 
and recesses and the flat anode will vary less proportionately for 
large than for small distances between anode and object. 

Too acid a bath gives less resistance, and tends to the develop- 
ment of too strong a current. Too little acid has the reverse 
effect. Copper deposited with too weak a current is crystalline 
and brittle. 

A general rule is to have the surface of the anodes equal to 
that of the objects to be plated. 

All such rules are only general. Thus, the question of excess 
of acid only applies to the limited number of baths in which free 
acid is present. Most baths are of alkaline reaction. 

The Relative Position of Anode and Surface to be Plated has 
its effect on the result. They should be as nearly parallel as pos- 
sible on general considerations. But there is a tendency for the 
lower parts of the objects to receive the thickest coating, as the 
solution tends in use to become more dense at the bottom of the 
bath. This tendency is counteracted by changing the position of 
the pieces, by moving them constantly, which is often done by 
power, and by agitating or stirring the solution in the bath. 

When an object is quickly plated, these precautions are unneces- 
sary. But when objects remain a long time in the bath, streaks 
are liable to appear on their lower area if they are not moved, or 
if the liquid is not stirred about. 

The tendency of metal to be deposited most thickly on parts 
nearest to the anode leads to the following rule: When a piece in 
high relief is to be plated, the anode should be as far removed as 
is possible from the object. The anode can be increased in area 



ELECTROPLATING. 671 

to compensate for the greater distance. Especially is this main- 
tenance of distance important when the solution is of such 
nature as to attack the object to be plated. In such a case it 
may attack the object in its deep parts while metal is being de- 
posited on its high places. A long distance as above is sup- 
posed to give a better quality of deposit as regards flexibility. 

Sometimes for very high relief auxiliary anodes carried on 
supporting wires into the deeper parts of the relief may be used 
to secure the deposition of metal there. 

Temperature of Baths.— The temperature of the baths has an 
Important effect. For some baths heat is prescribed; for others, 
no heat is required, but they are to be used at the ordinary tem- 
peratures. Sometimes it is necessary to prevent the formation 
of insoluble deposits on the anode. These deposits may become so 
thick as to prevent the passage of any current. 

The best way of heating the bath is to place the vessel fn an- 
other larger one containing water. The water in the outer vessel 
is heated, so that the whole arrangement constitutes a water-bath. 
Or the bath may be placed on an iron tray filled with sand, which 
is h-eated. This constitutes a sand-bath. The sand enables the 
vessel constituting the bath to be more evenly heated than if it 
rested on an iron plate in more or less imperfect contact with it. 

Material of Vessels.— For dipping baths for sulphuric acfd a 
lead-lined tank may be used. For alkaline dipping sheet-iron or 
cast-iron vessels are excellent. For nitric or hydrochloric acfd 
earthenware or gutta-percha vessels are best. Glass, enameled 
earthenware, varnished wood, or gutta-percha-lined wood are 
good materials for the plating baths. 

Metal Molds. — Sometimes for reproducing articles molds are 
required. These gfve the reverse of the article. By depositing 
by the electric current a thick coating of metal on them, the 
mold is produced in reverse, which is the true reproduction of the 
original article. Molds are sometfmes made of fusible metal. 
The following is an alloy suitable for the purpose: 

Kismuth 28 parts 

Tin 10 parts 

Lead 19 parts 

This alloy melts a little below the boiling point of water. 



672 ELECTRICIANS' HANDY BOOK. 

One way of using it for the reproduction of metals or coins 
is to melt it and pour some into a slight depression in a slab of 
marble. It will lie there in a flattened globule and will stay 
liquid for some time. The medal or coin to be reproduced is 
chilled and dried and is dropped flat upon the globule from a 
height of two or three inches. After the metal has solfdified, the 
medal is separated by light jarring. An exceedingly delicate mold 
is thus produced, on which the plating is executed. Only a slight 
hollow fn the marble is required to retain the melted metal. 
Another alloy is the following: 

Bismuth 250 parts 

Tin 125 parts 

Lead 160 parts 

Antimony 30 parts 

This alloy is used in a pasty condition, to which it is brought by 

proper degree of heating. It is then applied to the object. After 

cooling, a light yet decided blow will separate the two. The mold 

is then ready for its deposit. 

Wax and Stearine Molds. — These are more generally used than 

metal molds. 

Simple white wax or stearine may be melted and poured over 
the surface of the object, which latter has been previously ofled 
with a little olive oil. The wax must be allowed to cool several 
hours before any attempt is made to detach it from the original. 
Another way of using wax is to soften Tt by heat and to press the 
object into it. Other formulas are given, such as the following: 

Spermaceti 225 parts 

Beeswax ' ^0 parts 

Mutton tallow 50 parts 

Plumbago may be mixed with these compositions with benefit. 
White lead in dry powder gives still better results. 

The wax mixtures serve especially for the reproduction of flat 
objects, such as medals, coins, or for electrotyping. 

Plaster Holds.— The object is covered with a thin coating of 
olive oil. Plaster of Paris mfxed to a cream with water is painted 
on with a brush, and after perfect contact of plaster and object 
has been thus assured, the rest of the plaster is poured on. It 
may be held in place by a band of paper. 



ELECTROPLATING. 673 

Elastic riolds. — For difficult pieces the plaster mold can some- 
tfmes be applied in sections, which are then put together after re- 
moval. This is not always an easy thing to do. Elastic molds 
are often used for such cases. These are made by mixing a strong 
solution of glue with molasses, about four parts of glue solution 
to one of molasses. By heating together a perfect mixture is 
obtained. This softens when heated, and on cooling becomes elas- 
tic, like a very stiff jelly. It is melted and poured over the object 
to be molded, A box may he used to hold the object and to pre- 
vent the composition from running off. Sometimes threads are 
led along the surface of the object, secured by glue, if necessary 
with long ends. They are drawn away through the composition 
when ft has set, and divide it into sections. 

This composition can be used on undercut and complicated ob- 
jects. It springs out of shape on being drawn off, and springs 
back at once. 

Qutta=Percha Holds. — Gutta-percha softens in hot water, can 
be pressed upon an object so as to give the most delicate outlines, 
and is indefinitely durable. Gelatine or glue compositions such as 
just described may give finer results, but do not form durable 
molds. Alcohol, acid, and alkaline solutions are without effect 
on gutta-percha. It is worked by being softened in hot water 
and pressed upon the object to be copied. When the object is of 
such a shape that the gutta-percha will not leave it, application of 
hot water will soften it enough to permit it to be removed, and 
as it cools it will retain the form given it by the object. 

In using any of these materials, personal experience counts 
for a great deal. 

Preparing flolds.— The molds of non-conducting materials just 
described have to be given a conducting surface. Such are glue 
mixture, plaster, or gutta-percha molds. Plumbago is generally 
used for giving this quality to them. The mold is moistened a 
little, by steam if of plaster, and the plumbago is applied by a 
soft brush. It is rubbed on until the surface is bright and me- 
tallic in appearance, and of uniform luster. 

Copper powder is often mfxed with the plumbago. It can be 
made by putting lumps of pure zinc into boiling and saturated 
solution of copper sulphate. The zinc is soon covered with the 



674 ELECTRICIANS' HANDY BOOK. 

copper precipitated. The lumps of zinc may be removed and the 
copper brushed off, washed, and dried. This powder can be 
used alone. 

Sometimes fine iron powder is dusted over the surface • after 
plumbago has been applied. On dipping into a solution of copper 
sulphate, metallic copper is precipitated by the iron, and helps 
to give a good surface for plating. 

It is to be noted that deposition of metal spreads on all sides. 
If it begins energetically, in one spot, it spreads as well as 
builds up, and this action tends to produce even results. 

Varnish. — Red sealing wax dissolved in alcohol is an excellent 
varnish for coating parts of objects on which no deposit is desired. 
Thus the sides and backs of the molds of fusible metal must be 
varnished to prevent deposition where it is not desired, and where 
it would prevent removal of the metal deposited. 

Oiling. — For reproductions on metal molds, the surface must 
be slightly oiled to prevent adherence. Too thick a coating of 
oil will prevent the deposition of any metal, and makes the pro- 
cess inoperative. 

Placing Molds in the Bath.— The general system is to place 
the molds vertically as near as may be and opposite to the anode. 
Sometimes the mold is placed horizontally below the anode. One 
objection to this arrangement is that if any dirt or scale is de- 
tached from the anode, it will fall upon the object and impair 
the result. 

If metal molds are used, all connections of the anode should 
be completed before the mold is introduced. If not, there is 
danger that the mold may be attacked by the solution and oxi- 
dized. If the mold, connected to the zinc plate of the battery or 
equivalent wire of the plating dynamo, is introduced after the 
anode is in place, its introduction into the bath will be the last 
thing to complete the circuit, and it will be at once covered with \ 
a thin coating of metal. This is enough to prevent the mold I 
from being attacked. | 

Plating on Holds. — In using non-conducting molds, it is well i 
to begin with a current of low intensity. The deposit begins near 
the points of attachment of the conductor, and spreads laterally 
as already described. If hydrogen is disengaged, the coating will 



ELECTROPLATING. 675 

be brittle, and to prevent this generation of hydrogen the current 
is started at low intensity. A wire may be used as electrode until 
the mold is pretty well covered with the deposit. 

If air bubbles are seen in the interstices of the mold, they can 
be removed with a camel's hair pencil or other soft brush. 

Backing Up Deposits. — A thin deposit will suffice in reproduc- 
ing hollow objects, if it is strengthened by fusible brass or spel- 
ter such as is used for brazing. This can be put into the interior 
of the reproduction in small pieces with some borax. The blow- 
pipe is then used to heat the whole to redness. The spelter runs, 
and is n;iade to spread all over the surface by inclining the mold 
from side to side, so that it attaches itself to all the interior 
surface. The copper although thin resists the heat much longer 
than the spelter. It must be remembered that there is some 
danger of the spelter attacking and alloying with the copper and 
thus destroying the reproduction. Too long applied and too 
high heat will do this, and it will occur the more easily as the 
copper is thinner. If the copper is about one-tenth of an inch in 
thickness, there will be little danger of such an accident. 

Plating on QlasSv — A good deal of this work has been done 
recently, bottles especially having silver deposited upon them 
in various open-work designs and engraved as desired. Several 
methods have been used. Originally a varnish or lacquer was 
painted over the entire surface of the vessel on which the metal 
was to be deposited. When almost dry, plumbago was dusted over 
it, and it was polished with a soft brush. It was then wired, 
connected to the tank wire, placed in the tank, and left there 
for about eighteen hours' operation of the electro-plating current, 
or until a sufficient thickness of metal was obtained. The snow- 
white deposit of silver was polished. The designer then took it 
in hand, and painted a design with wax on the surface. The 
article was then immersed in an acid bath, and the silver not 
covered with wax was dissolved. Diluted nftric acid would an- 
swer for this operation. The engraver finishes the process by 
putting in any lines desired. 

The plumbago with the lacquer formed a black background, 
which w^s undesirable. A more recent process has been substi- 
tuted for the one described. Nitrate of silver solution mixed 



r 



676 ELECTRICIANS' HANDY BOOK. 

with dextrose solution is poured over the article. Silver is de- 
posited by reduction. Any of the methods of silvering used on 
astronomical reflectors, or so frequently used now on mirrors, 
can be employed. In this way an exceedingly thin coating of me- 
tallic silver is deposited all over the surface of the article. The 
electroplating is done upon this, and the processes detailed for 
the plumbago system are applied. 

Finally, a metallic oxide has been applied with some varnish- 
like agent following the design. On baking the oxide is reduced, 
giving a metallic coating for the electroplating. 

Practical Processes.— It must be kept in mind that in these 
as in other electroplating processes a description is not sufficient 
to enable operations to be successfully performed. Every felec- 
troplater has methods of carrying out processes which he has 
acquired by practice, and in many instances these methods are 
kept secret. A piece of plating may present an excellent ap- 
pearance, yet on use the metal may scale off. A considerable 
interval of time may be required to show defects. It is there- 
fore important when a good and satisfactory process is evolved 
to stick to it, and not to be too anxious to try something new.- 



CHAPTER XXXVIII. 

TELEPHONY. 

Sound.— Sound fs due to vibrations of matter, generally or al- 
ways vibrations of masses of matter. Thus a piano produces 
sound by the vibrations of its strings. A pair of cymbals dashed 
together vibrate, and produce sound. A plate of iron acted on by 
electro-magnetic pulses of attraction vibrates, and produces sound. 
The latter is the telephone receiver. 

Pitch.— Sounds vary in pitch. Some are high and some low. 
The sounds of high pitch are produced by relatively high-fre- 
quency vibrations, sounds of low pitch by low-frequency vibra- 
tions. The lowest note in a church organ may be due to 16 vi- 
brations and the highest to over 1000 vibrations per second. 

Fundamental Note. — Every piece of metal or other solid has 
a note which is produced if the whole piece vibrates as a whole, 
and is called the fundamental note. If two pieces are of equal 
thickness and of the same material, the larger one will have the 
lower natural or fundamental note. This follows out the law of 
strings; the longer string in a piano has the lower note. 

Overtones. — When a string in a piano is struck by the hammer, 
a number of notes are produced. The note due to the motion of 
the whole string in one arc of vibration back and forth is pro- 
duced, and is called the fundamental note^ due to what we may 
call n vibrations. Besides this the string produces notes of 2n, Sn, 
and other multiples of the fundamental note. The sound due to 
2n vibrations is one octave higher, that due to in vibrations is 
two octaves higher, and many notes of intermediate value are 
produced every time a piano string vibrates. These high notes 
are called "overtones." 

Sounding Plate,— The bottom of an oil can pushed in and al- 
lowed to spring out produces a sound due to its motion as a 
whole. In some sense it is a fundamental; at least it represents 

677 



678 ELECTRICIANS' HANDY BOOK. 

the mechanical action of a half-vibration in each of fts motions. 
If by some process a plate of metal can be made to vibrate as a 
whole, it would produce its fundamental note. Its motions would 
resemble those of the bottom of a spring-bottom oil can. Then 
if in addition the plate could be made to vibrate back and forth 
in a quarter of its area, as if divided by two lines at right angles 
to each other, one quarter springing up while the adjacent one 
sprang down, an overtone would be produced. If in addition to 
this the total surface vibrated in areas of one-eighth a still 
higher overtone would be produced. 

The Human Voice when it produces musical sounds is very 
rich in overtones. When it speaks, a very complicated vibration 
of various fundamentals irregularly succeeding each other, and 
complicated by all sorts of higher-pitch vibrations in addition 
to what may be called the fundamentals, is produced. It is not 
exactly a case of overtone production, but of simultaneous vibra- 
tions of a number of pitches produced by the vibrations of the 
vocal organs. 

Principle of Telephone Receiver. — In the telephone a plate of 
iron is acted on by impulses of attraction and release from attrac- 
tion. These impulses vary in periodicity and intensity exactly as 
do the vibrations in the human voice. The impulses force the 
plate into vibrations identical in frequency and relative strength 
with those in the human voice. The plate in producing these 
vibrations does not vibrate as a whole, but is forced to divide 
itself into areas of vibration. The natural vibration period is 
not the controlling factor. The plate has to correspond to the 
pulses of current going over the line and through the coil of the 
telephone. 

The pulses of current act upon the iron plate through the 
intermediation of an electro-magnet. The receiving instrument 
contains an electro-magnet connected to the transmission line. In 
front of the pole of this magnet a plate of iron is held very near 
to the pole. The pole faces its center. The changes in current 
passing through the coil are reflected in the attraction it exerts 
on the magnet. The variations in attraction, which may be many 
iiundred in a second, force the plate into corresponding vibra- 
tions. The plate vibrates in subdivisions of its area, which sub- 



TELEPHONY, . 679 

divisfons vary with great rapidity in number, areas, and shapes. 
A low note may make the plate vibrate in three or four areas, 
while simultaneous higher notes divide it into a quantity of 
smaller areas which vibrate without interfering with the large 
areas or with each other. 

Such is the vibration of the telephone plate. It is easier to 
think of when we picture the complicated vibrations of a string 
producing a fundamental tone and a lot of overtones. But the 
telephone plate only gives its natural or fundamental note by 
chance coincidence. The magnetic attraction forces it into vi- 
bration often quite unnatural to it, and such as cannot be referred 
to its natural periodicity of vibration. 

The Telephone Transmitter. — The above describes the theory 
of the telephonic receiver. It is connected by a wire with a dis- 
tant instrument, which is spoken into and is called the trans- 
mitter. The original transmitter was an instrument which was 
a duplicate of the receiver. Two telephone receivers connected 
in an electric circuit can be used as a complete telephone system. 
The same instrument can act alternately as transmitter and re- 
ceiver. 

As transmitter, the above type performs the functions of a 
dynamo. The voice makes the plate vibrate in the same forced 
manner as described for the receiver. The movements of the 
plate, which acts as an armature of the magnet, induce currents 
of high frequency of impulse in the circuit, and the distant tele- 
phone reproduces them in its plate armature as described. 

The intensity of the vibrations of the plate of the receiver is 
very much less than that of the transmitter. In the old-time 
telephones the speaker shouted into the instrument in order to 
make himself heard at the other end of the wire. 

Invention of the Microphone. — Soon after the telephone was 
invented about 1876, the microphone was invented, and the great 
defect of the telephone was overcome. Shouting into the trans- 
mitter ceased to be a requisite. The microphone varies the re- 
sistance of the telephone circuit. A current is kept passing 
through it as long as it is in use. As the resistance of the circuit 
changes, the intensity of the current also changes. These changes 
act upon the plate of the receiver and make it produce sound. 



680 



ELECTRICIANS' HANDY BOOK. 



^JUlUMJI^__^ 



The changes in resistance are produced by the sound waves 
produced by the voice acting on the microphone. The distant 
receiver reproduces the sound of the voice. 

Hughes Microphone. — This is the original microphone, whrch 
has been modified indefinitely in the many telephone receivers 
which have appeared from time to time. Referring to the cut, Fig. 
508, C fs a board on which are screwed two blocks BB of hard 
carbon. Holes in the blocks receive the ends of a little rod of 
carbon A, which rests in its position quite loosely. The apparatus 
is placed in circuit with a battery as indicated, and with a tele- 
phone receiver. The least agitation to which the carbon rod is 

subjected causes the resistance of 
the microphone to vary. The varia- 
tion in resistance causes the cur- 
rent to vary, and a sound is pro- 
duced in the receiver. A fly walk- 
ing on the instrument will produce 
a sound with every footfall. If 
talked against, the sound of the 
voice will be reproduced in the re- 
ceiver more or less perfectly. 

The Blake Transmitter.— For 
many years the Blake transmitter 
was the classic telephone receiver. 
In it a highly-finished block or button of hard carbon and a bit of 
platinum are held in contact with each other. One is pressed 
against a metallic diaphragm, the other is attached to an arm capa- 
ble of moving back and forth. The primary circuit of an induction 
coil includes these two buttons, and the primary current, when- 
ever the transmitter is in use, passes through the buttons from one 
to another, and therefore depends on their contact for its comple- 
tion. When the mouth is placed close to the diaphragm and words 
are spoken, the vibrations of the diaphragm change the degree of 
pressure existing between the buttons, these changes exactly corre- 
sponding in form with the form of the sound waves. This variar 
tion of pressure causes changes in resistance, and therefore by 
Ohm's law in current also, corresponding in form with the sound 
waves. These changes of current acting on the distant receiver 




Fig. 508.— Hughes's Micro- 
phone. 



TjuLEPHONY. 



681 



cause its magnet coils to vary in excitation also in form corre- 
sponding to the original sound waves. 
This throws the diapnragm of the re- 
ceiver, which is of iron and is the 
armature of the magnet, into vibrations 
exactly similar in form to those of the 
transmitter diaphragm, so that speech 
is reproduced. 

The Blake transmitter depends on 
pressure changes. Whether these affect 
resistance by direct variations in pres- 
sure or by changes in the area of con- 
tact due to pressure is not certain. It 
is probable that both actions have a 
part in the phenomenon. 

The cut. Fig. 508a, shows the Blak© 
transmitter. A is the opening to be 
spoken into, closed by a plate of iron 
or other diaphragm E. At the end of 
spring F is a bit of platinum, which 
presses against the diaphragm. K is 
the carbon button carried by a brass 
block P at the end of a spring G. 
B B are pillars, to the upper one of 
which a heavy counter weight C is attached by a spring. The lower 
pillar carries an adjusting screw N. The pressure between the 
platinum and carbon button is thus 
regulated, and the freedom given by 
the spring M, which carries the contact 
button and platinum contact piece, 
adds to the sensitiveness. The cur- 
rent passes through the contact by the 
springs F and G. 

Loose Carbon Transmitters. — A 
variation in the Blake transmitter ap- 
pears in instruments with quite loose 
carbon contacts. Thus, two disks of 
carbon, each with a number of depressions in them, may be 




Fig. 508a.— The Blake 
Transmitter. 




Fig. 509.— The Clamond 
Transmitter. 



682 



ELECTRICIANS' HANDY BOOK. 




Fig. 510.— The Western Union Trans- 
mitter. 



supported face to face, one attached to a diaphragm. The disks 

do not touch. In each 
pair of depressions, 
which face each other as 
the disks are placed, is a 
little carbon sphere. 
These are thrown into 
motion by the voice, and 
act exactly like the orig- 
inal Hughes microphone. 
Sometimes little carbon 
cylinders are used. The 
cut. Fig. 509, shows the 
Clamond transmitter. 
tlunning Transmitter. 
• — The more modern type of receiver which has met with most 
favor in this country, is of the so-called Running type. This in- 
ventor substituted for the vary- 
ing contact of a few pieces of 
accurately-shaped carbon, the 
varying contact of a quantity of 
granular carbon or carbon dust. 
It is on this basis that the mod- 
ern transmitter is constructed. 

In the cut. Fig. 510, is shown 
an exceedingly simple embodi- 
ment of this idea. To the right 
of D is a diaphragm, back of 
which is a second parallel plate 
B; the space between them is 
half filled with carbon dust C. 
The rest explains itself. This 
transmitter is of importance as 
Involving the use of granulated 
carbon instead of regularly- 
shaped pieces. 

Edison's Telephone.— This is 
shown in Fig. 511. E is the mouthpiece and D 




Fig. 511.— Edison's Telephone. 



the metal dia- 



TELEPHONY. 683 

phragm. I is a carbon disk with adjusting screw V. A platinum 
plate B B with an ivory button & is attached to the carbon disk. 
The ivory button is pressed against the diaphragm. C C is an in- 
sulating ring. The connections bring the disk into the circuit, 
and the resistance is varied when the instrument is spoken into. 

The Solid Back Transmitter.— This modern instrument con- 
tains essentially the following parts: Two small disks of polished 
carbon face each other. They are in a cylindrical case of diam- 
eter slightly larger than their own. Their faces are maintained 
near together, but not touching each other. One is attached to the 
diaphragm, which is fn modern instruments often made of alu- 
minium. The wires from the primary of the induction coil go, 
one to one disk and the other to the other. The space between 
the disks and any space left in the cylindrical case Is filled with 
fine carbon dust. 

The action is similar to what has been described. The pressure 
exerted on the carbon powder by the disks is changed by the 
vibrations of the diaphragm. The powder is also agitated. One 
or both of these actions produces the changes in resistance, to 
which the transmitting power of the circuit is due. Which action 
is the prevailing one, or what degree of efiiciency is to be ascribed 
to each, is uncertain. 

The Receiver.— Modern telephone receivers are of several types 
of construction. The straight hand telephone embodies the fol- 
lowing points in its construction: 

Within a hard-rubber cylindrical case is a compound perma- 
nent horseshoe or U-shaped magnet. A more powerful magnet 
is produced by clamping together several thin steel magnets than 
where the magnet is made of one piece of steel as thick as the 
combined thinner ones. A lamellar or compound magnet is there- 
fore the best. This magnet has its limbs so close that it fits into 
the standard India-rubber case. At its end are pole pieces pro- 
jecting in line with its limbs, and on these are placed coils or 
spools of fine insulated wire, wound like coils on a horseshoe mag- 
net oppositely to each other. 

At its forward end the cylindrical case carries an expansfon, 
somewhat like the mouth of a trumpet, over whose front a hard- 
rubber cover with a central aperture is secured by a thread cut 



684 ELECTRICIANS' HANDY BOOK. 

in the rubber. It screws on like tlie cover of a box. "When in 
position it holds a disl^ of iron across the mouth of the tube very 
close to the magnet poles. The disk closes the aperture in the 
cover. 

It is essential that the distance from disk to magnet poles 
shall be invariable. If the magnet were secured by its distant 
end, changes of temperature would constantly cause this dis- 
tance to vary as the metal of the magnet expanded and con- 
tracted. In the older receivers this defect was present. The 
magnet was secured by its distant end to the case; sometimes it 
was fastened at both ends. In the latter case changes of tem- 
perature were liable to produce damaging strains. 

In the modern instrument the magnet is fastened by its forward 
^end only. The four or five inches of steel extends back into the 
case, and is free to expand or contract without affecting the ad- 
justment. The critical distance between pole faces and metallic 
disk is invariable. 

The bobbins are wound with very fine wire. One of the early 
troubles with receivers was the breaking of this wire. In the 
modern instruments it is protected absolutely from all strain. 
Through the bottom of the handle, closed with a solid disk of 
India-rubber, pass two binding screws. Within the case these 
connect to two heavy pieces of insulated wire, which by being 
twisted together or other simple arrangement, are held fast, so 
that the upper ends cannot be moved by any manipulation of 
the binding screws. The upper ends are connected to the ter- 
minals of the windings of the bobbins. This secures the fine 
■wire from all strain. The telephone receiver is secure from all 
possibility of a broken circuit. 

The working parts of a modern telephone receiver are shown 
in Fig. 512. The two limbs of the magnet are seen held parallel 
to each other, with their upper ends connected by a block of cast 
iron. On their forward ends are the two bobbins. The plate of 
iron is held by a screw cover across the opening of the cup, 
within which the coils are seen. The screw cover forms the part 
of the case which is held against the ear of the person receiving 
the message. 

The Telephone Induction Coil.— The telephone transmitter is 



TELEPHONY. 



685 



placed in the circuit which includes the primary circuit of an 
induction coil and the exciting battery. This circuit is of far 
lower resistance than that of the long telephone line and of the 
coil or coils on the transmitter would be. In this fact lies one 
great incentive to its use. The sound waves vary the resistance 
of the microphone or transmitter, for the modern transmitter is 
invariably a microphone. If the transmitter is in a circuit of low 
resistance, its variations in resistance will be larger propor- 
tions of the total resistance of the circuit than if the total 
resistance of the circuit were high. A variation of 1/100 ohm 
on a 5-ohm circuit would be a variation of 1/500 of the total 




Fig. 513.— Telephone Receiver. 



resistance. By Ohm's law such a variation would cause the cur- 
rent to vary 1/500 fn intensity. But if the circuit were of 300 
ohms, the 1/100 ohm variation would only be 1/30,000 of the total 
resistance, and would only produce that variation in the current. 

The use of an induction coil secures this feature. The primary 
of the coil and the battery for actuating it need only have a 
comparatively small resistance. 

Acting as the primary of the induction coil upon the secondary, 
the variations in current due to the microphone action of the 
transmitter induce potential changes in the secondary. This im- 
presses a much higher set of voltages upon its circuit, and a 
diminished current varying in intensity in proportion to the 
changes in the primary goes over the line. The receiver is 
wound for this current with many turns of wire, so that the 
action of the current on the magnetic field of the receiver is in- 



686 



ELECTRICIANS' HANDY BOOK. 



creased or accentuated. The slight current multiplied by the 
large number of turns of wire in the receiver gives a tangible 
number of ampere turns. 

The induction coil effects two things. It brings about a relative- 
ly hfgh variation in the current changes, due to microphonic ac- 
tion, and it enables a much smaller wire to be used for trans- 
mission. There are other things involved, into which this book 
will not go, affecting the capacity of the line, the relative qual- 
ities for clear transmission of a small wire with small current or 
of a large wire with correspondingly large current, and other 
similar points. 

In Fig. 513 B is a battery, T represents a transmitter, and P the 




Fig. 513.— Induction Coil in Telephone Circuit. 



primary of an induction coil, whose secondary is indicated by S. 
The telephone receiver R is brought into circuit with the second- 
ary of the induction coil by the line wire L L.'. This illustrates 
the place of an induction coil in a telephone circuit. 

The extension of the telephone is made much easier by the 
use of small wires. A lead-covered cable, not much over three 
inches in diameter at its bulkiest parts, such as joints, can accom- 
modate wires enough for fifty or more metallic circuits. In the 
country almost invisible wires can be carried overhead through 
long spans at very slight expense. The induction coil makes 
these practicable in service. 

Dimensions of Telephone Induction Coils.— The dimensions of 



TELEPHONY, 



687 



induction coils include the turns of wire in primary and second- 
ary, the size and length of wires, and the consequent resistances. 
The iron core made of soft iron wires is not generally stated. 
The best dimensions are determined by trial rather than by 
calculation. Coils are tested over various lengths of line with 
transmitters of the class eventually to be used in the service. In 
general, it has been found that a coil good for one distance was 
good for another. 

With the old Blake transmitter in this country an induction 




Figs. 514 and 515.— Telephone Induction Coil. 



coil of one-half ohm primary and 250 ohms secondary was used. 
An extreme case of a low-resistance coil has been used on long- 
distance lines in this country. This one had a primary coil re- 
sistance of 0.3 ohm and a secondary coil resistance of 14 ohms. 
The ratio or resistance in the first case was 1 to 500, in the second 
1 to 46. The last-described coil had a very large core. 

The following are the dimensions of a typical modern coil for 
ordinary work: Core about 5 inches long and 9/16 inch in diam- 
eter, composed of 500 strands of No. 24 American gauge soft 
Swedes iron wire. The core is contained in a thin tube of fiber 
with square wooden heads or flanges at the ends. The primary 
coil is wound on the tube. It is composed of No. 20 wire, and two 



688 



ELECTRICIANS' HANDY BOOK. 



layers are wound in 200 turns. Paper is wound over it some 
layers deep, and the secondary is wound on this. It consists of 
two lines of No. 34 wire making 1,400 turns. The resistance of 
the primary coil is 0.38 ohm, of the secondary 75 ohms. This 
gives a resistance ratio of about 1 to 19 and of turns 1 to 7 only. 
Large wires are connected to the windings, and secured so as to 
prevent any strain coming on the windings. 

Figs. 514 and 515 give a sectional view and side view of a 
modern cofl with its primary coil and secondary coil wound on a 
core, consisting of a bundle of iron wire. 





Fig. 516.— Bracket Telephone. 



Fig. 517.— Induction 

Coil, in Bracket 

Telephone. 



Induction Coils in Bracl^et Telephones. — Coils are sometimes 
placed in the bases of swinging bracket telephones. Fig. 516 
shows such a telephone, and Fig. 517 shows the section of the 
chamber at its base, within which the induction coil is placed. 

Effect of the Telephone Induction Coil.— The universal use 
of induction coils shows that they are valuable in telephony. The 
ratio of reduction of -current is not so great as it would seemsihat 
it might be. 

They exercise an effect on the current also. The microphone 
current is uniform in direction, but of varying intensity. Ky.^^he 
induction coil this current is changed to an alternating one. 
The direction during the increase of microphone resistance is in 



TELEPHONY. 



689 



one direction, and during the decrease in the other. When the 
microphone is inactive, a steady current passes in the microphone 
circuit if the receiver is off its hook, while in the secondary induc- 
tion coil circuit under this condition no current whatever passes. 

In modern central battery practice they can no longer be con- 
sidered to have much effect in reducing the size of line wire, ow- 
ing to the absence of any battery at the customer's telephone ap- 
paratus. 

The Telephone Magneto.— The bell magneto has already been 
spoken of in this book. Although not part of a telephone sys- 




Figs. 518 and 519.- CAiiLiNG Magneto. 



tern strictly speaking, so many have been and still are in use as 
calling apparatus that some description must be given of them 
here. 

The magneto used for calling the central office consists of a 
field composed of several U-shaped permanent magnets, between 
whose poles a single-coil armature is rotated by turning a handle. 
On the shaft of the handle is a cogwheel which actuates a much 
smiller one on the shaft of the armature, so as to give it a suffi- 
ciently high speed of rotation. Two sprocket wheels and chain 
are sometimes used for the same purpose instead of gear wheels. 
Figs. 518 and 519 show a magneto generator, and Fig. 520 shows 
its armature core, 

Some device is usually applied to cut the armature out of cir- 



J 



690 



ELECTRICIANS' HANDY BOOK. 




cuit when not in use. Sometimes the shaft of the large gear 
wheel is free to move in the direction of its length a short dis- 
tance. In one position which it takes when at rest, it makes con- 
tact with the wire and short-circuits the armatur-e. When the lat- 
ter is to act, then the turn- 
ing of the handle automati- 
cally shifts the shaft a short 
distance, and breaks the cir- 
cuit, so that all the current 
passes through the armature. 
The shifting of the axle 
may be effected by the use of 
a cylindrical cam on which a 
projection on the shaft rides up. This cam may be formed on the 
hub of the large gear wheel, which wheel is so mounted that it 
cannot move along the line of the shaft, while the shaft can move 
back and forth through the aperture in its hub. In Fig. 521 this 
apparatus is illustrated. The large gear wheel C carries the cam 
on which the pin P rides up, shifting the shaft to the right and 
breaking the contact be- 

G 



Fig. 620.— Abmature Core op Mag- 
neto Bell. 




ft^3 



tween its end and the 
spring O. 

The magnets in this 
generator, made by the 
Western Telephone Con- 
struction Company, are 
made of magnet steel, 
in cross section % inch 
by % inch, and are bent 
into shape cold. The 
air gap, which is the 
distance from the arma- 
ture surface to the surface of the magnet poles, may be as small 
as 1/100 inch. A cast-iron core turned so that it fits with this 
slight clearance between the poles is wound with insulated 
w^ire. The pole pieces of the magnet are attached to the ends 
of the magnets, and are bored out to form a chamber for the 
armature to revolve in. 



X 



Fig. 531.— Automatic Magneto Switch. 



TELEPHONY. 691 

Many different magnetos have been constructed, differing only 
in detail. The current produced is alternating and of the sine 
type approximately. The bells which are mounted on the face of 
the magneto case are rung by a hammer operated by an electro- 
magnet with polarized relay. 

The armature is in improved constructions made of laminated 
type, built up of thfn disks held upon a shaft. The pole pieces 
are sometimes laminated also. 

The armature of the 10,000-ohm magneto is wound with No. 35 
or 36 American wire gauge silk-covered wire. The classification 
of magnetos is based on the resistance of a Ifne through which 
they can ring a bell. The figure such as 10,000 ohms above ex- 
presses line resistance, and has no direct reference to the di- 
mensions of the magneto. The resistance of the armature of the 
above magneto may vary from 400 to 550 ohms. The magnets of 
the bells are wound with No. 31 American wire gauge wire to a 
resistance of 75 to 100 ohms. Silk-insulated wire is used for 
winding. 

These dimensions apply to magnetos used on series work. But 
sometimes calling bells are connected across a circuit like lamps 
in parallel. Such arrangement is called in telephone practice 
bridging work. For this work a high inductance in the bell 
magnets fs required to prevent the rapidly alternating speaking 
current from going through the coils. It must be shunted 
through the receiver in parallel with the bell magnet coils. The 
generator for bridging work should have a stronger field than that 
of the one just described, with a longer armature wound with No. 
33 wire to about 350 ohms. The bell magnets are wound to as 
high a resfstance as 1,000 ohms with No. 33 single silk-covered 
wire, or to 1,200 to 1,600 ohms with No. 38 wire. The thing prin- 
cipally wanted is not resistance, but inductance, so that they shall 
act as choke coils for the speaking current. 

In central stations large magnetos or alternators are driVen 
by power and kept constantly in action. Current for ringing is 
taken from them by the operatives as required. 

Polarized Bell.— This is the bell which is rung by the magneto. 
It is shown fn Figs. 522 and 523. The electro-magnet has an 
armature pivoted below it, and to the center of which the clapper 



692 



ELECTRICIANS' HANDY BOOK. 



of the bells is attached. The armature is a bar of steel, and is 
magnetized so as to have a north pole at one end and a south 
pole at the other. When an alternating current from the mag- 
neto passes through the windings of the magnets, their strengths 
change with each alternation of current, so that the polarized 
armature swings first one way and then another, thus keeping 
the clapper in motion, so as to ring the bells placed within its 
range of motion. 

Telephone Systems. — ^The general installation of a telephone 
system includes these elements: A microphone, termed the 
transmitter, is the apparatus spoken against. This is in a cir- 
cuit through which a current flows when the transmitter is in 




Figs. 532 and 523.— Polarized Armature Belt,. 



use. On this circuit is a source of potential which maintains the 
current. Generally, this circuit includes the primary circuit of 
an induction coil. There is a secondary circuit of the induc- 
tion coil, which is in circuit with the receiving instrument. The 
receiver, as it is called, is a modification and only a slight one of 
the Bell telephone of twenty-five years ago. To effect electrical 
connection between different customers, there is a central station. 
Wires from the customers' houses go to the central station, and by 
means of one or more switchboards communication between any 
two customers is brought about in a few seconds. Finally, call- 
ing apparatus fs included. In the houses of customers this gives 
an audible signal, generally the ringing of a bell. In the central 



TELEPHONY. 



693 



office a shutter is dropped, making a click and exposing the num- 
ber of the customer, or else in more modern practice an in- 
candescent lamp at the customer's number on the switchboard is 
lighted when a call is made. 

In many systems at the present day there is a battery in every 
customer's house. In more modern practice all the current is 
supplied from a storage battery at the central station. Protec- 
tive devices to secure the system from lightning and damage from 
crosses with other wires are among details which form in mod- 
ern practice essential parts of the system. 

House Connections. — The house connections for a telephone 




Fig. 534.— House Telephone Connection. Hook-Switch Depressed. 



instrument with private battery have been variously carried out 
from time to time. A diagram of a typical system is given in 
the cuts. Pigs. 524 and 524a. L.L.' are the lines, M the magneto, 
C the call bell, T the transmitter, B the customer's battery, P 
and S the primary and secondary of the induction coil, R the re- 
ceiver, and the hook-switch on which the transmitter is hung 
when it is out of use is seen on the left of the coil. 

The first position shown is that in which the hook-switch is 
down. This is brought about in practice by hanging the receiver 
on the hook-switch. The illustrations show the circuit, including 
the receiver, induction coil, battery, and transmitter, and the con- 
necting line &, all of which are thrown out of circuit when the 
hook-switch is depressed and connects with the stud 3. 



694 



ELECTRICIANS' HANDY BOOK. 



An alternating current sent over the line from the central sta- 
tion goes through the magneto armature coil, then through the 
bell, ringing the latter, and by way of the hook-switch and stud 
3 and connecting wire a back to the other line L'. 

In this position, if the handle of the generator is turnedj an 
alternating current will be sent over the line and will ring the 
bells at the central station or will operate any form of signal ap- 
paratus employed there. 

The receiver fs not shown on the hook, in order to make the 
diagram clearer. It is supposed to be hung upon the hook-switch. 

On hearing the call the customer unhooks the receiver, and the 
hook-switch springs up. It opens the circuit at 3 and closes the 




h M 



^ 



3 hi^ ^A/VvA-J 



Line L 



M u.. 



Fig. 



-House Telephone Connection. Hook-Switch Raised. 



circuits at 1 and 2. The cut. Fig. 524a, shows the connections thus 
brought about. What before were inactive wires become active. 
The magneto and its bell are cut out of circuit. 

Tracing the connections on this diagram, it will be seen that 
the receiver is now in circuit with the line U, and through the 
secondary S of the induction coil with the line L. A message 
can be received by it. The transmitter is in circuit with the 
battery and primary of the induction coil. The circuit contain- 
ing these three is closed through the contact 2 and the hook- 
switch. The hook-swftch acts as a conductor for both primary 
and secondary currents from the induction coil, and as conductor 
for the talking current from the distant instrument. In the posi- 



TELEPHONY. 



695 



tion shown, the primary coil of the induction coil is on closed 
circuit, and a direct current goes through the transmitter. 

When the transmitter is spoken into, the primary current 
varies as described, and the secondary current induced goes 
through the receiver to the line L U, and through the hook-switch, 
connection 1, line 6, to the other line L. 

Series Telephone Circuit.— 'This is shown in Fig. 525. The 





Fig. 535.— Series Telephone 
Circuit. 



Fia. 526. 



-Bridged Telephone 
Circuit. 



line wires connect at 1 and 3, When the hook-switch is depressed, 
the bell B is in circuit with the line and the magneto M is short- 
circuited. When the customer operates his generator this short 
circuit is automatically opened. When the hook-switch is de- 
pressed the receiver R is also cut out of the circuit. The connec- 
tions are now adapted for calling up by the bell B only. 

On unhooking the receiver R, the hook-switch L springs up, 
opens the bell circuit, and closes both the circuit of the transmit- 
ter T with the primary P of the induction coil in circuit with it 
and the circuit of the receiver R with the s-econdary S of the in- 



696 ELECTRICIANS' HANDY BOOK. 

duction coil in circuit with it. The connections are now ready to 
transmit and receive. 

In this cut and in Fig. 526 central binding posts 2 are shown. 
These are for connecting to the ground for the lightning arresters. 

Bridged Telephone Circuit.— Circuits of this description are 
characterized by the fact that the bell is connected across the 
lines permanently. A bridged circuit is given in Fig. 526. The 
bell C is permanently connected between the lines 1 and 2. Its 
magnets are wound of high resistance and have high inductance. 
Whether the hook-switch H is up or down, the bell circuit is in 
the same connection, being quite independent. But the resistance 
and reactance of its magnets make it an effectual barrier to tele- 
phonic currents; for them it is a choke coil. The magneto^ M is 
in a second bridged circuit, normally open, but closed when, the 
handle is turned. These are parts of the calling circuit. The 
talking circuit with the receiver R in circuit with the secondary 
S of the induction coil is a third bridge circuit, open when the 
hook-switch is depressed. 

When the telephone is taken off the hook, it rises and closes 
the talking circuit and also the local transmitting circuit. In 
the latter the primary P of the induction coil, the transmitter 
T, and battery B are included in series. 

A switch is shown at k at the magneto. This is supposed to be 
operated by hand to close the magneto circuit when the central 
is to be rung up. An automatic closing device similar to that 
already described for the magneto is also used. 

The Hook-Switch." — Considerable thought has been expended 
on the best construction of the hook-switch. Platinum connecting 
points or studs are the best, and it is an object to have a little 
sliding action as they open and close with the rise and descent 
of the switch. This tends to keep the contacts in good condition 
and free from dust. The contact action is only due to gravity 
when the receiver is hung up, and to a spring when the receiver 
is removed and the hook-switch springs up. If the contacts do 
slide, they should slide only on a conducting surface, not on an in- 
sulating surface and then on a conducting one. Sliding contacts 
brfng about cutting as one of their objectionable features. 

If platinum contacts are used, sliding contacts are not neces- 



TELEPHONY. 697 

sary; for such metals as brass they are requisite. To prevent 
cutting, it is a good plan to make the two surfaces of dissimilar 
metals, just as in steam engine and heavy machine practfce. The 
use of brass surfaces with German-silver springs, sliding as they 
make contact on the brass, is considered good practice. Sometimes 
the lever or hook-switch arm forms no part of the circuit, but 
it generally does. The journal or pivot screw should not be de- 
pended on as part of the cfrcuit, but should be reinforced by a 
flexible wire twisted into a spiral spring, with its ends soldered 
one to the base, and one to the switch arm. It is well to pass the 
ends of the wire through holes and solder it in them after burring 
or riveting its ends. 

Common Battery Systems. — The most advanced system of tele- 
phone installation has no local batteries in the house sets of tele« 




IT IT. 

Fig. 537.— Common Battery MetaxiLic Circuit System. 

phoning apparatus. In very many installations the local battery 
is still employed, and the circuits hitherto shown in this book 
have embodied it. 

The simplest representation of a metallic-circuit common bat- 
tery system is shown in Fig. 527. B is the battery at the central 
station. This is always a storage battery. At P are plug switches. 
The line drawn through the center of each switch indicates insu- 
lation of the two sides of the plug from one another. When the 
plugs are inserted, the two line transmitters T and receivers R 
and the battery are all thrown into circuit. It will be understood 
that the house connections are here omitted, the receiver and 
transmitter merely indicating them. They follow the general 
lines of those used with the local battery. 

The system is shown in this cut as applied to several sub- 
scribers. The low resistance of the battery prevents any notice- 
able amount of current being deflected from one circuit into the 
other. 



698 



ELECTRICIANS' HANDY BOOK, 



Sometimes choke coils are used between the central battery 
and the subscribers' lines. These coils permit the passage of di- 
rect current from the battery, which gives the basis for the trans- 
mitters to work on. The choke coils cut off all chance of inter- 
communication between independent circuits. 

Stone's Common Battery System. — The diagram. Fig. 528, 
shows two circuits supplied from a single battery B. The coils 
used are of but slight resistance compared to that of the rest of 
the circuit, but are of considerable impedance. The battery main- 
tains a direct current through any of the circuits it is plugged 
into or connected with. The transmitter when talked into causes 
this current to vary, and a speaking current is thus produced, 
restricted practically to its own circuit by the inductance of the 
coils. This inductance resists the passage of an alternating or 




Fig. 528.— Stone's Common Battery System. 



undulatory current, such as that of the speaking type produced 
by the microphonic action of the transmitter. This system is 
due to John S. Stone. 

Dean's Common Battery System.— A most ingenious applica- 
tion of the choke coil enables both lines of a metallic circuit to 
be used in parallel for sending current to the transmitting circuit 
with a ground return. The diagram. Fig. 529, gives the general 
features of the system. 

The central station battery B is grounded. It connects from 
its other terminal to the center of a choke coil I whose winding 
is connected across the two leads of the metallic circuit. At the 
subscriber's end of the circuit another choke coil, I, is connected 
across. From its center a connection fs taken to a local closed 
circuit, including the primary of an induction coil and a trans- 



TELEPHONY. 



699 



mitter. A ground connection is taken from a point of tlifs cir- 
cuit opposite to tlie other connection and between transmitter and 
primary of the induction coil. 

From the battery when all connections are made a direct cur- 
rent goes through the two branches of the choke cofl I to both 
leads of the metallic circuit. It goes through both of these in 
parallel and through both parts of the choke coil I to its central 
connection. Thence it goes through both branches of the closed 
primary of the coil in the transmitter circuit to the ground. In 
this closed circuit the current divides. Part goes through the 
primary p of the induction coil, but without effect, as it is a con- 
stant current. Part goes through the transmitter T. 

These variations in current through p, due to the voice acting 




Fig. 539.— Dean's Common Battery System. 



on the transmitter, induce a speaking current in the metallic cir- 
cuit, which includes the secondary s of the induction coil, and the 
receiver R at each station. The inductance of the choke colls pre- 
vents any of the talking current going through them, so that the 
circuit for talking purposes is a true metallic one. 

By the use of choke coils on the same principles it has been pro- 
posed to have local storage batteries in»the subscribers' sets, and 
to charge them from the central station. The use of choke coils 
enables the two lines of the metallic circuit to be used in parallel 
for the charging current with a ground return. The parallel cir- 
cuit thus given is of one-half the normal resistance of the line. 
The current flowing in the same dfrection in both leads at the 
subscriber's station divides between the storage battery on one 
side and the transmitter with a special resistance coil on the 
other. The resistance coil and transmitter with their resistances 
in series shunt most of the current through the storage battery. 



700 ELECTRICIANS' HANDY BOOK. 

Party Lines. — The expense of a telephone distribution system 
is materially diminished by grouping private stations which are 
near to each other in groups of four or more, and serving them 
all with a single circuit from the central office. The first thing 
involved is the calling up of any one subscriber of the groups 
from the central station without calling up the others. 

Polarized Bells for Party Lines. — In some systems polarized 
bells are used. The general principle of these may be given in 
a few words. 

One type of polarized bell is one whose magnet armature is a 
permanent magnet, and which is attracted to the electro-magnet 
by current in one direction and repelled by that in another. If 
a current in the direction which attracts the armature is sent 
through the magnet coils, the armature will move toward the 
magnet poles and the striker will strike the bell. If the current 
ceases, it will be drawn back by the spring. An intermittent 
current in one direction will keep the striker in vibration, and 
the bell will ring continuously. If the current is in the other 
direction, it will repel the armature only and no ringing will 
be produced. 

The bells in two of the subscribers' houses are connected tO' 
one lead of the circuit only, and are grounded from the other 
terminal. These bells are oppositely polarized. By sending a 
ringing current in one or the other direction, either bell can be 
rung as desired. 

On the other lead of the main circuit two more bells, also op- 
positely polarized, are connected and grounded, each at a sub- 
scriber's house. By using this lead and sending ringing currents 
of opposite directions, either of these subscribers can be called up. 

The four bells by this arrangement can be individually rung 
from the central station. 

Eight bells can be individually rung by calling upon variation 
in current strength as well as polarity. 

Four polarized bells wound to high resistance are connected 
exactly as described, on the four most distant stations. These 
can be rung by a light current one at a time as desired. 

At the nearer stations four polarized bells are connected in 
series, two oppositely polarized on each lead. These are wound 



TELEPHONY. 701 

to low resistance, and are not actuated by the slight current 
which rings the further bells. But if a strong enough current 
to ring one of them is sent, a relay situated beyond them is 
actuated and grounds the line at that point. The bell at the 
nearer station is then rung through the ground connection, which 
connection cuts out the bells beyond the house in question. In 
any case, only one of these would be rung, on account of its 
polarity and of the direction of the current. 

Suppose that a line is fitted with four polarized bells as de- 
scribed on page 700 for four separate subscribers' stations. Using 
both lines in parallel, as if they were one, two oppositely polar- 
ized bells can be connected thereto and grounded. They can be 
operated exactly as the two bells on either lead of the line. The 
full metallic circuit can be utilized for two more bells. This 
gives eight subscribers on a single circuit. 

In practice this system is operated by ordinary bells actuated 
from a local battery. The bell and battery are connected in 
a local circuit opened and closed by polarized and neutral relays, 
differently connected as regards their polarization, there being 
two relays for each station and bell. 

The armatures of both relays at a house must be released 
from attraction and rest against their back-stops to cause their 
bell to ring. The operator by sending current in one or the 
other direction over one or the other of the leads, or over both 
in parallel, can ring any of the eight bells. One arrangement 
is to utilize six of the single-wire and through circuit connec- 
tions for subscribers' signals, and to use the remaining two 
for locking the hook-switch, so that the central office cannot be 
called when the line is in use by another subscriber. 

Harmonic Signal for Party Lines. — The armature of an elec- 
tro-magnet can be mounted with a flat straight spring in place 
of a pivot. Such an armature if pulled to one side and released 
will swing back and forth and vibrate at a frequency depending 
on its weight, the length and the stiffness of the spring. If a 
series of impulses are imparted to it, coinciding in frequency 
with its ov)^n natural frequency, it will be caused to vibrate. If 
the impulses are irregular or have no correspondence with the 
periodicity of the armature movements, they will give it some 



702 



ELECTRICIANS' HANDY BOOK. 



motion perhaps, but not with the same energy as if they harmon- 
ized with each other. 

If through a magnet facing the armature impulses were sent, 
they would have little effect on the armature unless their 
frequency corresponded with that of the magnet. If their 
frequency was one-half or one-quarter or other integral fraction 
of that of the armature they would affect it, but would have 
most effect if of its exact frequency. Such series of impulses of 
current would start it into vibration. A contact point must be 




Fig. 530.— Harmonic BELii Signal. 



provided with which the armature will make contact as it 
vibrates. By this contact a bell circuit is to be closed. For 
each closing the bell will ring. As long as the armature vibrates, 
the bell will ring in unison. 

The cut. Fig. 530, shows the general idea of such a harmonic 
signal. The magnet C receives the current broken into impulses 
of definite number per second. When this number corresponds 
with the natural number of vibrations of the armature B, carried 
by the flat spring screwed on the top of the block &, the armature 
will vibrate, and only then. 

If it vibrates, it will close the bell circuit at the point n, where 



TELEPHONY. 703 

there are two contacts, one on B and one on D. "When this con- 
tact is closed, the bell rings. 

The armature B will not he thrown into vibration by a broken 
current whose impulses do not correspond with its own natural 
period of vibration. By having armatures of different rates of 
vibration at different subscribers' houses, any subscriber can be 
called by a broken current of frequency corresponding to that 
of his armature. 

In some systems the vibrations are used to close a bell circuit 
as above, in some to open a shunt in parallel with the bell, and 
which when closed prevents it from ringing by taking the cur- 
rent. In some the bell-hammer and armature are one. 

The harmonic system is very little used in American tele- 
phone practice. 

A practical limitation exists to the number of subscribers that 
can be served by one wire, because the amount of service ex- 
acted by four to six subscribers is about all that one line can 
take care of. If harmonic calls were used, only four to six 
rates of current impulses would be needed at the central station. 

Distributing Boards. — A central telephone station may have 
six thousand or more individual circuits entering it. Every 
one of these has to be taken to its place, where a number is 
assigned it on the main switchboard, which in all large offices is 
of the multiple type. The mass of wires back of the main 
switch is complicated, and if it had to have its connections 
changed and shifted about, endless confusion would result. To 
avoid the necessity for changing the wires at this point, a 
special arrangement called a distributing board is used. It pro- 
vides two faces or boards, separated a little from each other. 
On one face are secured all the wires of the circuits which enter 
the building. These connections are supposed never to be dis- 
turbed under ordinary conditions. 

A multiple switchboard has a number of identical panels. 
Each panel has plug sockets for all the circuits that enter the 
building, with perhaps one or two thousand others to provide 
for future extensions. 

Circuits from the multiple switchboard equal in number to 
the sockets on one panel of the board run to the other side of the 



■704 ELECTRICIANS' HANDY BOOK. 

distributing board. As the panels of the multiple switchboard 
all are connected. No, 1 to No. 1 and so on all the length of the 
board, it follows that every connection on the distributing board 
connects with every panel of the multiple switchboard. 

It does more than this. Taking No, 1 connection from the 
distributing board, this wire connects with every No. 1 plug on 
the switchboard. There may be fifty or more panels, on each 
panel a single No. 1 plug and all connected to one circuit. This 
circuit goes to No. 1 connection on the distributing board. The 
same is done for every socket on each panel; a connection from 
all of each given number runs to a corresponding number on 
the distributing board. 

These connections are normally never disturbed. 

The space of some feet in depth intervening between the 
front and back of the distributing board is bridged across by 
wires, one for every active connection on the switchboard.- 
These wire connections are subject to frequent change. If it is 
necessary to change a subscriber's number, the wire from his 
connection to the distributing board is connected to the other 
face of the board, to the connection leading to the desired sets 
of numbers on the multiple switchboard. 

The shape the distributing board takes is a sort of open 
rectangular rack. Several feet intervene between the two faces, 
and within this space the connections are made. There is little 
that is distinctive about them. Each one has to have front and 
rear connections corresponding in number, and on the face next 
to the switchboard they must correspond in designation with 
the sockets on each panel of the multiple switchboard. 

A wire circuit enters the building, and is connected to the 
rear of the distributing board. It may be decided to connect it 
to the set of sockets numbered 75 on the multiple switchboard. 
By short wire leads within the distributing board the con- 
nection from the incoming wire to the No. 75 connection on the 
other face of the distributing board is made. This one connec- 
tion puts the subscriber whose wire circuit is thus disposed of 
in connection with every plug bearing the number 75 on the 
multiple switchboard, as well as with the calling plug for the 
operator. 



TELEPHONY. 



705 



Fig. 531 gives a cross section and view of the side of a dis- 
tributing board. At C a cable from the street is supposed to 
enter. Its end is opened, and wires tv are taken from the cable 
head H and carried to the near face of the board. Wires from 
the other face run to the plug connections S S on the switch- 
board C. Wires called bridle or jumper wires connect the front 
and rear connections of the distributing board with each other. 

The board illustrated is the Hibbard board. The frame is open 
work built of iron pipe, forming a sort of trellis. 




Fig. 531.— Distributing Board. 



It has been aptly said that the object of the distributing board 
is to concentj'ate the changes of connections into a definite local- 
ity. The short wire connections are of No. 20 to 22 wire tinned, 
rubber-covered, and twisted in pairs to give the elements for 
continuing the metallic circuit. Lightning arresters are often 
included in the connections. The best and generally accepted 
practice is to solder all the jumper wire connections. 

Repeating Coils. — The repeating coil used in telephone practice 
is an induction coil. Its core is made of a bundle of annealed 
iron wire. Its windings are generally of the same number of 
turns and of the same size of wire for both primary and second- 



706 ELECTRICIANS' HANDY BOOK. 

ary circuits or windings. It is used to cause the speaking cur- 
rent in one line to be transferred to another. It has four binding 
posts — a pair for each circuit. 

Thus a ground telephone circuit may extend to a certain point 
in the district and there terminate. Its end may be connected 
to one terminal or binding post of the coil, whose other corres- 
ponding binding post is grounded by another wire connection. 
To the other pair of terminals are connected the ends of a metal- 
lic telephone circuit. 

Any conversation on the grounded line will be transferred to 
the metallic circuit by induction, and the reverse action will also' 
take place. Thus, a circuit may be part grounded "and part 
metallic. 

One principal use of this combination is to avoid interference 
from other lines, and not have the expense of a full metallic cir- 
cuit system. Where there is no danger of interference a ground 
circuit is used, with one winding of the repeating coil in series at 
its outer end. For the part where interference is feared a metal- 
lic circuit is put in, with the other winding of coil in series. By 
another repeating coil a ground circuit may be brought into the 
circuit again if the area of disturbance and interference is passed. 
There are other uses of the repeating coil in central station prac- 
tice. 

The Multiple Switchboard is used in central telephone ex- 
changes to effect the connection of one subscriber with another. 
If there were but one or tv/o hundred subscribers in a district, 
the connections between them could be effected by a single board. 
On the board the terminals of all the subscribers could be placed 
and each one numbered. A flexible wire with proper end con- 
nections could connect any subscriber's terminal to any other. 

If there were some thousand subscribers in a district, it would 
be impossible for a single operator to answer all the calls which 
would come in from them. Therefore, it would have to be de- 
termined what number of subscribers could be attended to by 
a single operator. Each operator would have a calling-up board 
or set of connections to a limited number of subscribers. These 
subscribers would be able to call up this operator and no other. 

Calling-up connections for the entire number of subscribers 



TELEPHONY. 707 

are arranged along the full length of the switchboard. The 
number that one operator can take care of are arranged within 
reach of the arm as the operator sits on a chair or high stool. 

For each subscriber there is only a single calling-up connec- 
tion. This portion of the switchboard is single, not multiple. 

Each operator must without leaving the chair be able to con- 
nect any one of the limited number of calling-up connections, 
which may vary in different cases, to any one of the subscribers 
in the whole district, who may be several thousand. In front of 
each operator is a panel of the board, with a connection on it 
for every one of the subscribers, and all these connections within 
reach of the arm. Corresponding in width with the panel is the 
row of calling-up connections. If there are fifty operators, there 
are fifty panels. Every connection of a given number on one 
panel is repeated there fifty • times along the series of panels. 
This multiplication of panels constitutes the multiple feature 
of the switchboard. 

13345 13345 13345 13345 13345 

6789 10 6789 10 6789 10 6789 10 6789 10 

11 13 13 14 15 11 13 13 14 15 11 13 13 14 15 11 13 13 14 15 11 12 13 14 15 

16 17 18 19 20 16 17 18 19 30 16 17 18 19 30 16 17 18 19 30 16 17 18 19 30 

31 33 33 34 25 31 33 33 34 35 31 33 33 34 35 Si 32 33 34 25 21 22 2S 24: 25 

12 3 4 5 6 7 8 9 10 11 13 13 14 15 16 17 18 19 30 21 33 33 24 35 

The diagram shows the relation of panels to calling-up con- 
nections, and also indicates the multiple connections for identi- 
cal numbers of the series of panels. Each panel is shown with 
twenty-five subscribers' connections, and five calling-up connec- 
tions are shown for each panel. This is as if each operator was 
only called up by five subscribers, and as if there were only 
twenty-five subscribers in the district. In reality there might be 
several thousand connections on each panel, and fifty to two 
I hundred calling-up connections for each panel. Each panel in- 
dicates one operator; as above shown, there would be five. The 
total number of subscribers divided by the number of panels 
gives the number of calling-up connections to one operator. The 
number of panels fixes the number of operators, and under each 
panel are the number of calling-up connections, each one for a 



708 ELECTRICIANS' HANDY BOOK. 

designated subscriber, which that particular operator must 
answer. 

The number of calling-up connections which one operator can 
attend to depends on the number of subscribers. When there 
are a large number of subscribers connected to a central station, 
each one will call for more connections in a day than if there 
were only a few. If a subscriber has six thousand co-subscribers 
at a station, he will call up more times in a day than if he only 
had one thousand or five hundred. Therefore, as the number 
of subscribers in the district served by the central station is 
larger, the calling-up connections assigned to each operator must 
be fewer in number. 

The number of operators required on a multiple switchboard 
does not increase in simple ratio. Doubling the number of sub- 
scribers exacts more than double the number of operators. The 
rate of increase approximates to the geometric ratio. 

The above simple description merely gives the outlines of 
the theory of the multiple switchboard. As it comes in practice 
when there are several thousand subscribers to be included in 
every panel, and where the panels have to be consequently very 
numerous, the complication becomes enormous. 

There are a number of modifications designed to bring about 
more efficient working. 

Operation of Switchboard. — Calling-up connections of the sub- 
scribers on a multiple switchboard are operated by the sub- 
scriber. When the handle of his magneto is turned, or when the 
receiver is removed from the hook-switch as the case may be, a 
current is sent over the line. At the calling-up connection on 
the switchboard in the central station this current operates some 
kind of annunciator to indicate the number of his station to 
the operator. 

The Mechanical Annunciator is a falling shutter or drop, seen 
in so many forms in ordinary house-bell annunciators, in hotel 
annunciators, and the like. 

A little shutter hinged at the base is held up in a vertical 
position by a catch or hook which holds its upper edge. The 
hook is operated by an electro-magnet. When the magnet is 
excited by a current passing through it, it attracts an armature 



TELEPHONY. 709 

to which the hook is attached. This raises the hook, and the 
shutter at once drops. On its inner surface is painted or other- 
wise marked the nuniber of the subscriber's station to which its 
circuit is connected. The current sent over the circuit by the 
distant subscriber drops the shutter and discloses his number. 
The operator replaces the shutter by hand as soon as the magnet 
releases its armature, so that the retaining hook drops to its 
lowest position. The drop is now ready for another call. 

Such annunciators are used in great number. An advance is 
made by having an electric system of replacing the shutter. 

It is considered that automatic setting of the annunciators 
effects a saving of time and energy for the operator, who is often 
worked to the full extent of her power during the busy hours 
of the day. Where mechanical annunciators are used, the ten- 
dency is to use self-restoring drops. 

Lamp Annunciator. — The most advanced practice on switch- 
boards is to substitute incandescent lamps for mechanical drops. 
Eight- to twenty-volt lamps are used, one for each calling-up con- 
nection. A simple low-voltage lamp represents the maximum of 
simplicity and takes the place of the mechanism of the drop, 
inevitably more or less complicated. Lamps are cheaper than 
the modern self-restoring drops. They operate when current 
passes, and cease when it ceases, thus presenting the self-restor- 
ing feature of the most improved drops without complication of 
the latter. Lamp signals are rapidly coming into use on the 
larger and more important switchboards. At first very low 
voltage lamps were used. These proved quite unreliable; they 
were very sensitive to slight changes in voltage, were hard to 
make, and burnt out very easily. Ten- to twenty-volt lamps are 
now frequently used. 

To produce the lighting current a storage battery at the central 
station is used. This gives an almost constant voltage. By 
having the lamps of reasonably high voltage, a drop or rise of a 
fraction of a volt has a much less effect on the duration of a 
lamp than when they are of only two to four volts potential. 
One-half of a volt on a two-volt lamp is twenty-five per cent of 
its voltage. On a twenty-volt lamp it is only two and a half per 
cent. 



710 



ELECTRICIANS' HANDY BOOK. 



In one system the removal of the receiver from the hook- 
switch throws the lamp into circuit with the station storage 
battery. The lighting current goes through the whole line, and 
through the transmitter at the subscriber's station. 

Several objections have been cited in reference to this sys- 
tem. The valid one is that if a cross occurs between lines, a 
very low resistance circuit may be produced, through which 
current will reach the lamp. The low resistance will operate 
to burn out the lamp. A very obvious way to dispose of this 
trouble is to put the lamp on a relay circuit. The calling cur- 
rent closes the relay, and the lamp is lighted from the storage 




Fig. 532.— Spring Jack. 



battery through the unchanged resistance of the local circuit. 
Apparently more complicated than the straight circuit system, 
the relay system avoids the necessity of adjusting the resistances 
of long and short circuits so as to give each of the lamps the 
proper current. 

Spring Jacks. — Connections to subscribers' lines on multiple 
switchboards are made by the agency of plugs thrust into spring 
jacks. Some boards have between one and two hundred thou- 
sand spring jacks. Fig. 532 illustrates the principle of construc- 
tion of one kind. The spring jack is screwed to the back of the 
board, and a tube in its front projects through it. When the 
plug is withdrawn, the spring f rests on the contact screw p, 
and a closed circuit is made through the spring jack. When 
the plug is pushed into place, it pushes the spring up from the 



TELEPHONY. 



7H 



contact screw, opening the circuit and connecting its own lead 
thereto. 

The front of a telephone switchboard appears full of holes, 
regularly spaced, and along the middle level appears a straight 
row of such holes extending its whole length. These are the 
spring jacks. On a five-panel board each subscriber will have 



Line Jacks 



Line Drops 




Subscribers Lines 



Clearing-out Drop 




Fig. 533.— Switchboard Connections. 

six spring jacks; five are on the face of the board and one is in 
the horizontal row. 

Various constructions of spring jacks are in use. They may 
act to give a simple metallic contact, or if the plug is in two 
divisions insulated from one another, a double connection may 
be made by plugging the hole. A flexible wire ("flexible cord") 
is connected to the plug. 



Jj 



712 ELECTRICIANS' HANDY BOOK. 

Switchboard Connections. — The diagram, Fig. 533, illustrates 
the work of a switchboard. Two subscribers' lines are shown 
entering an exchange, each including in its circuit an annunci- 
ator drop. When the subscriber by magneto or otherwise sends 
a current over his line, his special annunciator drop falls and 
discloses his number. Spring jacks such as have just been illus- 
trated are indicated, one for each line. It will be seen how in 
their closed position, which is when the plugs are not inserted, the 
spring jacks act to complete the circuit through the annunciators 
to the earth at G. 

In the lower part of the diagram are shown the switchboard 
connections. R and T are the receiver and transmitter used 
by the operator; B is the local battery, which with the trans- 
mitter T is in circuit with the primary p of an induction coil. 
P P' are plugs to go into the spring jacks at the top of the cut. 

Assume tha;t a subscriber desiring to use the telephone has 
by means of his magneto sent a current through his line. It 
drops the shutter of an annunciator, disclosing his number. 
The operator inserts the plug P' into the subscriber's spring 
jack. Each spring jack, it will be understood, has its number, 
that of the subscriber to whom it belongs. When the plug is 
inserted in the socket with the same number as that shown 
when the shutter drops, the subscriber is cut off from the ground 
at G, and is connected in circuit with the operator's receiver 
R and secondary S of his induction coil to the ground at G'. 
Immediately on inserting the plug, the key K", which has been 
hitherto open, is closed, completing the circuit described. The 
operator by the transmitter T asks the number desired, and 
the subscriber tells it. The operator receives it by the receiver 
R. The plug P is inserted into the spring jack of the subscriber 
who is to be called up, and the key K is depressed. By work- 
ing the magneto M the bell of the second subscriber, the one 
who is to be called up, is rung. When the second subscriber 
has answered, his answer being received by the operator's re- 
ceiver R, the keys K and K" are opened, and the subscribers are 
in circuit with each other, and can speak together. The oper- 
ator can listen by closing or depressing the switch K". 

When the subscribers are through they both probably ring 



TELEPHONY. 



713 




off, although it would be just as good if only one did so. This 
sends a current through the coil of the magnet of the annunci- 
ator, called the clearing-out drop. Its shutter drops, showing 
that the conversation is finished. The plugs are pulled out of 
the spring jacks, and the lines are again ready for work. 

The proportion of plugs for a 
given number of subscribers is 
a matter for consideration. 
One pair of plugs for every ten 
subscribers is a proportion 
which in many cases is found 
advantageous. 

Lamp Signal System.— A 
simple presentation of the lamp 
signal annunciator system is 
given in Fig, 534. The sub- 
scriber's apparatus is shown in 
the upper part of the cut at 
B, and the central oflEice con- 
nections in the lower part of 
the cut at C. At C, g and h in- 
dicate choke coils, I the annun- 
ciator lamp, and i a battery; g, 
h, and I are all in one metallic 
circuit. There is one such cir- 
cuit with numbered lamp for 
each subscriber. 

When the receiver is on the 
hook-switch, the circuit including 
the annunciator lamp I is closed 
through the high resistance 

of about 1000 ohms of the calling bell e. This cuts down the 
current so that the lamp Z shows no light. When the receiver 
is taken off the hook-switch, this springs up and closes a circuit 
as it does so by coming in contact with two terminals above it, 
as shown at C. This short-circuits the bell coils. In the short 
circuit is included the secondary of the subscribers' induction 
coil. But this short circuit may aggregate less than 50 ohms 



3^ 



Fig. 534.— Lamp Signal Switch- 
board Connection. 



714 ELECTRICIANS' HANDY BOOK. 

resistance, and the lamp is lighted. This calls the central sta- 
tion operator, who effects the desired connection, when told it by 
the calling subscriber. 

The local battery at the subscriber's house is a storage battery. 
When the hook-switch is released, this battery operates the trans- 
mitter. When the receiver is hung on the hook-switch, the 
secondary battery is in closed circuit with the coils of the calling 
bell magnet, and receives a slight charging current of about 
1/50 ampere. This keeps it in good condition for use. 

This description is of the simplest kind of lamp signaling 
system. There are many modifications, involving more compli- 
cated connections. 

If the local battery becomes too weak, the subscriber's trans- 
mitter will work with current from the central station battery, 
and the local battery will act as a sort of equalizer. 

In general practice, the calling lamp is on a relay circuit, and 
the relay closes its circuit when the receiver is taken off its 
switch, by short-circuiting somewhat as described above. 

Conduction Interference. ^Electric conductors such as line 
wires are sometimes subject to much trouble from induction and 
other electric disturbances. This is especially true of telephone 
lines. The telephone receiver is a wonderfully sensitive de- 
tector of any current change. It tells nothing if a constant cur- 
rent is passing through it, but reveals sudden changes in intensity 
of the current passing through it by producing a sound. Grounded 
circuits are peculiarly subject to disturbance. A grounded tele- 
phone circuit may be rendered quite useless by the presence in 
its vicinity of an electric trolley. The latter use the rails as 
their return circuit, and some of the current leaks into the 
ground and into grounded circuits in the vicinity. A grounded 
telephone line will sometimes sound in accord with the motions 
of the car motors. A part of the return current will go through 
the line, following the law of divided circuits. 

Induction Interference. — The above is a disturbance by con- 
duction. Sometimes induction from neighboring irregular cur- 
rents will affect a line. Insulation is without effect on induction, 
so whether the wire is insulated or bare, it will suffer disturb- 
ance as far as telephonic uses are concerned, A neighboring 



TELEPHONY. 715 

telegraph line will act on a telephone line, so that its signals 
will be heard in the receivers. 

Such induction is usually treated as electro-magnetic. Experi- 
ments go to show that it is electrostatic. If a telephone receiver 
is placed in the center of a line, and one at each end, the end 
receivers will give a sound when a disturbing circuit acts on 
the line, while the central instrument will be mute. Even if the 
line is cut in the center, the two halves will give current changes 
which will make the end telephones sound. 

The use of metallic circuits does away with much of this 



^ < > ><1 



sf- 



Figs. 535, 536 and 537.— Telephone Line Induction. 



trouble. If the disturbing line lay parallel with and between 
the two leads of the metallic circuit and equidistant from both, 
it would affect both leads equally and in the same direction, so 
that the two effects would neutralize each other. But in practice 
the disturbing line never occupies just such a position. One or 
the other lead is nearer to the source of disturbance than the 
other, and a disturbance results, which may be very annoying, 
particularly in telephone service. 

In Fig. 535 the heavy line indicates a circuit of varying cur. 
rent. The telephone circuit is seen parallel with it, with ona 
side nearer to it than the other. The nearer side of the tele- 
phone circuit will have the stronger potential impressed on it, 
and the result is indicated by the relative length of the arrows. 



716 ELECTRICIANS' HANDY BOOK. 

The induced current will be due to the difference of the electro- 
motive force on the two leads of the telephone circuit. 

In Fig. 536 the effects of an inducing wire equally distant 
from both the telephone leads is shown. Equal electromotive 
force is impressed on both leads and in the same direction. 
Therefore no current is produced, and the telephones are un- 
affected. 

In Fig. 537 transposition is illustrated. The wires are un- 
equally affected because of their different distances from the 
source of disturbance. If the result is followed out on the dia- 
gram, it will be seen that the net result is the impressment of 
equal electromotive forces on both leads of the wire and in the 
same direction, so that they neutralize each other. 

In induction the polarity of the electromotive force induced 
constantly changes. The arrows in these diagrams illustrate the 
condition at one instant of the induction. 

When a number of lines are carried on one set of poles, the 
transpositions of the lines must not be the same for all. If the 
identical transposition were given to all, there would be mutual 
induction. This induction is avoided by transposing the leads 
of the different circuits at intervals or at points varying for 
each pair of leads. Thus, two pairs of lines may be transposed 
at intervals of one mile for each case. To overcome mutual in- 
duction the places of transposition may vary, so that there would 
always be one-half mile between them. Other pairs could be 
transposed every half mile, and could also be varied in their 
places of transposition. 

Transposition on pole lines is effected by transposition insu- 
lators. These have two grooves. The wire is cut, and each 
end is turned about the insulator in its own groove. The same 
is done for the other wire of the circuit, and by short wires 
the rear end of one lead is connected to the forward end of the 
other, and the remaining ends are cross-connected in like man- 
ner. 

Twisting the leads of a circuit is much used. This secures 
comparative immunity from induction. In cables containing a 
number of pairs of wires twisting is extensively applied, and 
has been found to prevent induction. 



TELEPHONY, 



717 



Induction troubles are felt most on telephone circuits. Ordi- 
nary telegraph, power, or lighting circuits are relatively or com- 
pletely free from- them. The cable construction companies 
endeavor to supply non-inductive cables, and have much success 
in their construction. 




Fig. 537a.— PoiiE Connections for Subscriber's Circuit. 



Subscriber's Pole Connections.— The method of taking a sub- 
scriber's connection from a pole line is shown in Fig. 537a. A 
double-grooved insulator, such as referred to in the preceding 
paragraph, receives the ends of the line wire, which is cut at 
this point. From the ends a branch circuit is taken, as shown 
in the cut, two single-grooved insulators being provided, which 
take the strain off the main line insulator. 

Improvements. — No branch of electrical engineering is more 
subject to development and improvement than telephony. The 
utmost that can be done in these few pages is to give the outlines 
of what is a very complicated subject, much of whose theory is 
largely unformulated. Automatic exchange systems dispensing 
in part or in whole with the central station operators are coming 
to the front, and if they ever reach full development, may exer- 
cise profound influence on the future of the business, by introduce 
ing a different ratio of expenses to number of subscribers. 



CHAPTER XXXIX. 

BELL WIRING. 

Bell Wiring is a class of work in which bad insulation leads 
to endless trouble. 

Size of Wire. — Cheapness often induces the use of undersized 
wire, A small current will ring a bell, and the lengths of wire 
in a house are so short that the question of resistance hardly 
needsi to be considered. Undersized wire is objectionable be- 
cause of its weakness. Wire stapled to joists under a floor, and 
Ifcjd back of lath and plaster, seems out of all danger, but thin 
wire in house work will break and give much trouble. Circuits 
sometimes need changes; an extra bell, or more likely an extra 
pvish button, is to be put in. Thin wire is far less easy to con- 
nect, because it is liable to break and give the work of extra 
sjjlicing to restore it. Wire in houses is sometimes cut by 
tacks or nails. Heavy wire has at least a better chance of escap- 
ing this accident than thin wire has. 

Nos. 16 and 18 American wire gauge are standard sizes. When 
No. 20 or even finer wire is used, the standard of the work is 
greatly lowered. The wire should be double-coated and paraf- 
fined. This makes it slippery, which is a great advantage, be- 
cause the coating is not so much injured by pulling around 
corners as a wire without paraffin in its coating would be. This 
is an incidental advantage. The first object of the paraffin is to 
improve the insulation and to exclude dampness. 

In putting wires into a finished house, they have often to be 
led up or down between studding and back of the lath and 
plaster. The processes used are called "fishing." In executing 
this, the greatest care should be taken to avoid dragging the 
wire around a sharp corner. If it is unavoidable, the paraffining 
helps to save the insulation, 

718 



BELL WIRING. 719 

Fishing. — To run a wire behind lath and plastering, a space 
between studding must be found by sounding with a hammer. 
There is a slight difference, which to the practised ear discloses 
the hollow chamber or space. To lead a wire through it, a hole 
is bored through lath and plaster. A piece of very flexible 
string is used for the "fishing." Well-waxed sail twine is ex- 
cellent. Sometimes fishing line is used. Waxing is advisable 
for it also. To its end a weight is attached, for which purpose 
a few inches of No. 19 double jack chain is recommended. The 
flexible chain can be pushed through the hole, and doubling 
down will go through a small space. Often studs on a brick 
wall are only an inch thick, so that the chain is excellent for 
such places. A half dozen spherical lead bullets, bored and 
strung like beads, are better than the chain. With the weight 
at its end the cord is fed through the hole and goes down until 
it reaches the desired point, provided all is clear. With a plumb 
line or by the sound of the weight on the end of the cord the 
line is located, and a hole is bored through the wall or surbase 
or wherever it may be to meet it. A piece of wire with a short 
hook is inserted, and the cord is hooked by it and drawn out; 
the bell wire is attached to it, and is dravv^n back by the cord. 
This principle takes care of all vertical and often of inclined 
runs of wire. The wire can be drawn downward from the other 
end by the same cord. 

Work Under Floors. — In running wire under the floor, a steel 
spring or flat wire % by 1/64 inch, with a hook at its end called 
a snake or fishing wire, is used. This can be pushed quite a 
long distance horizontally, and the string or the jack chain at 
its end, which has been dropped through a hole in the floor at 
some distant point, can be caught by a hook at its end and 
drawn back. If the beams run in the right direction or with the 
wire, it facilitates floor work greatly. If they run in the other 
direction, which is across the line to be followed, the wire must 
be taken through the beams one by one. A beam is located, and 
a hole is bored from the floor diagonally down from a point 
above its center. Floor beams are about a foot apart. If the 
string is dropped through a corresponding hole at the next beam, 
it is readily flshed up to the surface of the beam in question. A 



720 



ELECTRICIANS' HANDY BOOK. 



second diagonal hole is then bored, through the beam, so as tO' 
form an inverted V, and the cord is passed down it, to be fished 
up from the next beam. The process and result is shown in 
the cut, Fig. 538. The hole must be nicely closed by putty or 
plugs. For very particular work the holes must be kept as small 
as is consistent with gettting the cord and fishing wire through 
them. 

This kind of work would not be allowed for fine-finished hard- 
w^ood floors, unless possibly a joiner would undertake to close 
the holes so neatly that the plugging would be unnoticed. Many 
cases would occur where this method would not be allowed. 




Fig. 538.— Fishing BelLi Wire Under Floor. 



All sorts of expedients may be adopted. Houses differ from 
each other. Some have clear spaces running from plate to sill. 
If they can be found, a heavier weight, called a mouse, may be 
dropped at the end of a string, and thus one fishing will take a 
wire from base to top story. More will be learned by a few 
weeks with a competent man than by any description. 

Moldings may be removed and the wires put back of them, 
grooves being raced out for the wires, or a corner may be 
planed off the lower inside corner of the molding to give room 
for the wire. 

Racing is cutting a narrow groove in a floor or other wooden 
surface with a tool called a racing tool. It consists of a handle 
into which blades with hooked ends can be inserted. The groove 



BELL WIRING. 721 

made is big enough to hold a wire. Sometimes wires can be 
laid in such grooves secured in place with tacks, but under ex- 
isting conditions of house construction and furnishing this is not 
so often allowable as formerly, when floors were of soft wood and 
were fully carpeted. 

Leading the Wires. — Exposed wires are used in some places, 
and are selected of color to match the paint or woodwork on which 
they lie. These can be stapled. The greatest care must be 
taken to keep them away from electric light wires. The distance 
between two parallel lines of bell wires should be half an inch, 
two wires never being put under one staple. Occasionally it may 
be necessary to adopt gutta-percha-covered wire for damp places, 
but this is not often the case. To splice wires, strip four inches 
of each and make the regular telegraph lineman's splice, as 
shown on page 508. If a very good job is to be executed, solder 
each joint, using no acid, but only rosin or some non-C0rro° 
sive flux. The joints may be taped, but this is not usually neces- 
sary. If the joints are not well soldered, so that the solder 
fails to cover the copper, paper should be wrapped around them 
before taping. 

Grounding Wires. — Some inches of the end are stripped of in- 
sulation and brightened by scraping or otherwise. They are 
wound around a gas or water pipe, the part being scraped or 
sand-papered. The place should be soldered. It is good practice 
to solder all grounded ends of the same system to gas pipes alone 
or to water pipes alone, and not to solder some to water pipes 
and others to gas pipes. In case of disconnection of a pipe sys- 
tem, the grounds will still be good. Thus bells could be rung 
during repairs to plumbing or gas pipes. The removal of the 
gas or water meter removes the water or gas system from the 
ground in great measure. 

Soldering. — For soldering joints between wires a rather hard 
solder, one containing more than half its weight of tin, should 
be used. The soldering iron may be filed to the shape of a wedge 
with a groove filed across it, about Vs inch deep. The groove in 
the hot and well-tinned soldering iron is filled with solder. The 
twisted joining of the wires is dusted over with powdered rosin 
or other non-corrosive flux, and the groove full of melted solder 



722 ELECTRICIANS' HANDY BOOK. 

is applied to its under side. The iron is rocked back and forth 
and ultimately turned completely around the wire, or else the 
wire itself is turned around while in the groove. Soldering 
joints is not universal, but it adds to the quality of an installa- 
tion. 

In all cases before joining wires use emery paper or some 
equivalent on the ends, so as to brighten them and remove cop- 
per oxide and dirt and secure good electrical connection. Solder 
will not take hold of a dirty surface. 

Wires. — Annunciator wire is double cotton-covered wire, with 
the cover saturated with melted paraffin. Office wire is a grade 
better in the quality of its cover. Sometimes wires are carried 
through tubes. As this brings them close together, wire of thor- 
oughly good quality of insulation should be used in this case. 

Distinguishing Colors may be used for different wires. This 
is a. regular practice in other branches of work, and in bell work 
wires covered with different colored insulations can be used to 
distinguish the runs of wire. Otherwise, more or less frequent 
tagging of the wires can be adopted to make them readily traced 
through the house. As the tendency is now to use exposed plumb- 
ing, bell wiring should be done as much on the exposed order of 
work as possible. 



I 



CHAPTER XL 

ELECTRIC HEATING. 

Electric Cooking and Domestic Heating is possible because 
the current need only be turned on a few minutes before it is 
needed, and can be at once turned off. If it were kept on by 
the day, the expense would be prohibitive. Various utensils re- 
quire a certain period of heating before cooking can be begun 
with them. For an electric stove or griddle a period of 5 to 8 
minutes is given; for a broiler, 12 to 14 minutes; for an oven, 20 
minutes. The cooking operations proper are about the same as 
for coal fires. For boiling water, 15 to 20 minutes, and for heat- 
ing flatirons, 8 to 12 minutes are required. 

The cost of electric cooking in one experiment was found to 
be about five times that of coal cooking. All such figures are 
approximations only, as circumstances vary so greatly. 

Power Required for Cooking. — A small broiler, 6 by 8 inches 
in area, will require from 340 to 400 watts, a 1%-pint kettle a 
little less; a 16-quart kettle, 1140 watts. A full electric range 
of 6 square feet area consumed 1650 watts per square foot of 
surface. 

Efficiency of between 80 and 90 per cent can be attained in 
boiling water. 

Electric Furnaces may be divided into two classes. In one 
the voltaic arc is the heating agency; in the other class incan- 
descence is the principal source of heat. With many materials 
both arc and incandescence may operate simultaneously. The 
illustration, Fig. 539, gives a cross section of a simple electric 
furnace. The square box or case may be of iron. It is lined 
with some insulating refractory substance, such as lime or mag- 
nesia. Carbon rods pass through holes in the box, and are in- 
sulated therefrom as shown. To operate such a furnace a strong 



724 



ELECTRICIANS' HANDY BOOK. 



alternating current is required. The carbons are connected in 
tile circuit, and an arc is started across the interval between 
them. This may be done by pushing the carbons together, and 
thus closing the circuit. They are then drawn apart, and the arc 




^^m 






h 



.mm 



Fig. 539,— Open Electric Furnace. 



Fig. 540.— Closed Electhio 
Furnace. 



is thus "struck" or formed. Material to be operated on is placed 
in the cavity, and as it reaches the level of the arc becomes 
heated by it. 

Although this describes arc heating, it may often happen that 
when the material reaches the level of the carbons it conducts 
the current, and the furnace operates by incandescence. 




Fig. 541.— Siemens's Flectbio Purnace. 



In Fig. 540 is shown an advance on the last. It is a covered 
furnace adapted to receive a vessel to be heated by the arc. In 
this apparatus, where the substance to be heated and the arc are 
distant from each other, there is no question of incandescence. 
The heat is due to the arc. 

The furnace shown in Fig. 541 is virtually a lined crucible 
through whose sides two electrodes project. The electrodes are 
mounted so that they can be run in and out, thus varying the 



ELECTRIC HEATING. 



725 



^^ 



length of the arc. Worm gear is provided for this purpose. One 
electrode is a carbon tube, the other is of metal and hollow, and 
water circulates through it, introduced by a pipe placed on its 
axis and reaching. nearly to its end. 

In the furnace shown in Fig. 542 a brick structure filled with 




Fig. 543.— CowiiES's Horizontal Ftjrnace. 





Fig. 543.— Cowles's Vertical 
Furnace. 



Fig. 544.--MECHANiCAii- 
liY Operated Electric 

Furnace. 



non-conducting material, such as sand, B, holds a retort A. At 
the left end is a carbon electrode C, and at the other end is a 
carbon crucible which acts as the other electrode. The crucible 
D is perforated at d to permit the escape of any gas generated in 
the reactions. 

The furnace of Fig. 543 has a hopper, through which material 
to be acted upon is introduced. From the bottom of the hopper a 



726 



ELECTRICIANS' HANDY BOOK. 



tubular electrode extends downward, and a second one rises from 
the bottom, so as nearly to meet the other. Material can also 
be introduced from outside the upper tubular electrode. Gases 
which escape are condensed or cooled in a condenser, indicated 
to the right of the furnace. As the charge melts it runs down 
the central opening of the lower electrode and is withdrawn. 
In Fig. 544 is given a section and plan of a more complicated 
furnace. In this structure the upper electrode can be moved not 
only up and down, but its end can be swung about over the area 




Fig. 546.— The Electric BiiOWPiPE. 



of the crucible below it, so that all parts of the charge can be sub- 
jected to its action. The crucible is below the end of the carbon 
electrode, and forms itself the lower electrode. It is carried on 
trunnions, so that it can be turned down for pouring out its 
contents. 

Another simple form of furnace is shown in Fig. 545. The 
crucible with its lining forms one electrode, and a carbon rod de- 
scends into its center from above, constituting the other electrode. 
Material enough may be added to cover the charge acted on and 
to supply new material as the materials melt down. 

The electric furnace is a very simple thing. The factor abso- 
lutely necessary for it is plenty of electric power. The furna'^ 



ELECTRIC HEATING. 



12,1 



used in the manufacture of carborundum has sometimes iJeen 
little more than a pile of 
coke covering the charge and 
held in place by a loose 
brick wall. Carbon elec- 
trodes entered the ends, and 
the current acting by incan- 
descence heated the charge to 
white heat. 

The Electric Arc Blow- 
pipe. — The voltaic arc is re- 
pelled when a magnet pole 
is brought near it. This prin- 
ciple has been applied to 
producing an electric blow- 
pipe, in which the arc driven 
to one side, as shown in Fig. 
546, is used like a blowpipe 
flame for local heating. 




Fig. 547.— EiiECTRio Abo Heating. 



Direct Heating by the 
Electric Arc is carried out 
by making the object to be 
heated one of the electrodes 
of the arc. Thus, a boiler 
is shown in the cut, Fig. 
547, as under treatment by 
the arc. One conductor is 
connected to it, the other 
is connected to a carbon rod 
carried in a holder and held 
over the point to be heated. 
An arc is caused to form, 
and is brought where de- 
sired by moving the carbon 
pencil over the spot. A 
colored glass screen pro- 
tects the eyes of the operative. The carbon holder has a 
handle with shield to protect the hand, something like the hilt 




Fig. 548,— Diagram of Arc Heating. 



728 



ELECTRICIANS' HANDY BOOK. 



of a fencing foil. A general diagram of tlie connections is given 
in Fig. 548. There is a storage battery, with a connection box U, 
by which the number of its cells supplying current to the arc can 



:x]i=<rz:^- 




Figs. 549 and 650.— El,ectric SoiiDERiNG Irons. 



be increased or diminished. W is a resistance frame, and the car- 
bon holder is at K. V is a voltmeter, and A is an ammeter. Be- 
low is seen the carbon holder with its protecting shield. 
The Electric Soldering Iron, Figs. 549 and 550, uses less than 

red heat. The first figure shows 
the external view of one, and the 
lower figure is a section. The 
copper bolt is surrounded by a 
coil of wire insulated by fire- 
proof insulation, which on the 
passage of a sufficient current 
keeps the bolt at the proper tem- 
perature for soldering. 

Electric Welding, the princi- 
ples of which are shown in Fig. 
551, uses the heat of direct in- 
candescence. An induction coil 
or transformer has two coils, a 
high- and a low-tension one. An 
alternating current is passed 
through the high-tension coil, 
in the low-tension coil a much more intense cur- 
but impresses a much lower voltage on the same 




Fig. 551.— Electric Welding. 



which induces 

rent than itself, 

circuit. In the cut the high-tension coil is the inner one lying 

flat on the paper, and the simple bar of iron outside it is the 



ELECTRIC HEATING. 



729 



low-tension coil. Wires are seen leading to the high-tension 
coil. These are connected to the source of supply. Two heavy 
coils of iron wire surround both coils and act as core. The pieces 
to be welded are held in the clamps as shown, and are rapidly 




Fig. 552.— Electric Incubator. 

heated by the induced current. By the screw they are forced to- 
gether so as to weld. Almost any conducting metal can be welded 
by this process. Very remarkable results have been attained 
with various metals and shapes. 




Fig. 553. -Electric Badiator. 



The Electric Incubator, Fig. 552, is a curiosity in electric heat- 
ing. A basket holds eggs and has a cover which contains a coil 
of wire, through which a current of electricity passes. By a ther- 
mometer the temperature is watched, and regulated by a resist- 
ance coil. The young chickens are kept in a coop which contains 
a heater to represent the mother hen. Both are shown in the 
cut, each with a thermometer on top. 



730 ELECTRICIANS' HANDY BOOK. 

Electric Radiator.— Many forms are made, consisting of long 
wire conductors which may be covered with asbestos insulation. 
The cut. Fig. 553, gives a simple form in which the conductor is 
carried up and down over studs on a frame. Iron and steel wire 
are good materials for the conductor. Their principal use is for 
heating electric cars. 

Economy of Electric Heating.— \Vhen electric power is pro- 
duced by a steam plant, the loss of energy is very great. By a 
law underlying the operation of heat engines, of which the steam 
engine is the most conspicuous example, by far the greater part 
of the potential energy of the fuel is wasted. From 90 per cent 
upward of the heat of the coal burned is lost. The law is termed 
the second law of thermodynamics. Under these circumstances 
the efficiency of electric heating is necessarily low. On the other 
hand, when water power is used for its production, it may be 
very efficient. 

Its economy when produced by a steam-driven plant is low on 
its face, but is relatively high when intermittent heating is in 
question. The current can be cut off so readily that long periods 
of useless expenditure of fuel, inevitable in many cases of heat- 
ing with coal, are avoided. The economy thus brought about 
compensates for the low efficiency explained above. 

The electric heating of trolley cars is possible because the 
power is rather advantageously produced and the repairs of 
stoves are avoided. 



CHAPTER XLI. 

WIRELESS TELEGRAPHY. 

Wave Transmission of Signals. — The ocean is thrown into 
waves by the motion of the air or winds. The particles of water 
in making the waves constantly move in vertical circles, round 
and round. The diameter of the circles is several times the 
height of a wave. The particles of water do not move forward 
or backward except through a limited range, and a wave on the 
deep sea does not transfer or carry water along with it. There 
is no displacement. A man at one side of a pond of still water 
could send a message to another by waves, if there was any 
good way of detecting them. The constant reflection and repe- 
tition of the waves would occasion trouble. But on a large stretch 
of water a sharp impulse given might send waves of water, which 
could be detected at a considerable distance. Such waves could 
be used to transmit messages. The air is thrown into waves of 
another type by the vibrations of bodies, and transmits sound. 
As air is much lighter than water, air waves travel at much 
higher speed than do water waves. About a thousand feet a 
second is the rate of sound transmission by air waves. The 
luminiferous ether is thrown into waves by various kinds of dis- 
turbances, electrical among others. Ether waves are transmitted 
with a velocity which would take them around the earth nearly 
eight times in a second. Air waves are the medium for propa- 
gating sound, such as the human voice. By wireless telegraphy 
ether waves are produced at one place and detected at another, 
and are made to transmit intelligence by the Morse code or some 
equivalent. The waves used are called Hertz waves, from the cele- 
brated Prof. H. Hertz, an early demonstrator in this field. Their 
existence was predicated on Clerk Maxwell's celebrated electro- 
magnetic theory of light. 

731 



732 ELECTRICIANS' HANDY BOOK,: ' 

If a discharge is produced between the terminals of an induc- 
tion coil, a spark as it has long been called is produced. In reality 
this is an enormous multitude of discharges or sparks beating back 
and forth with decreasing intensity, but uniform frequency. The 
time occupied by the multiple discharge is very short, but the dur- 
ation of a single element of it is in the second order of duration, 
and is almost infinitesimal. The discharge beating back and 
forth is called an oscillatory discharge. The time in fractions of 
a second of a discharge is calculated by the formula. T = 27t 
\/ KL\ K being capacity and L inductance of the circuit. The 
oscillation in Hertz oscillators, as the special circuits for these 
experiments are called, varies from 10,000,000 to 300,000,000 per 
second. If it were possible to increase them to a sufficient fre- 
quency, light would be the result. The trifling light given by the 
spark is due to the heat of the discharge, not to its oscillations. 

Hertz Receiver. — The oscillator transmits waves. As a receiver 
Hertz used a broken circle of copper wire. The diameter of the 
circle was about 16 inches. It terminated in little metal balls or 
knobs, whose distance apart was adjustable. When the oscillator 
was discharged, a minute spark passed across from ball to ball of 
the detector or receiver, when everything was in adjustment. 
The receiver only operated at a short distance. At more than 
the length of a room the effect wbs too attenuated to produce a 
spark in the detector. 

Branly's Coherer.— This iAvestigator found that loose metal 
filings were astonishingly f5ensitive to ether waves of slow fre- 
quency, such aE5 produced by oscillatory electric discharges. A 
tube containing loose metal filings and of relatively high resist- 
ance had its resistance greatly diminished by being held near the 
place where such ether waves could reach it. The ether waves 
make the loose filings take up a new condition and act in a de- 
gree like solid metal. As the molecules of every solid metal co- 
here, the tube of filings is appropriately termed a coherer. When 
once caused to cohere, the filings remained so until disturbed by 
agitation or otherwise. If such a tube is placed in circuit with 
a battery and relay, ether waves will by reducing resistance close 
the relay. If they cease, then tapping the tube will increase the 
resistance and open the relay. 



WIRELESS TELEGRAPHY. 



733 



w 



J3^« 



Wireless Telegraphy is based on the production of an oscil- 
latory discharge at a transmitting station, its transmission by 
ether waves through space, and the detection of the waves due 
to the discharge at the distant station. Originally only the 
coherer v/as used. It is still in extensive use, although many 
other receiving instruments have been invented. It is now 
sharing the work with other devices more rapid in action. 

Transmitting Apparatus. — The principle of the Marconi trans- 
mitting apparatus is shown in the cut, Fig. 554. One or more 
vertical wires, W, are supported by a mast or other support. 
The lower ends, if there are several wires, are joined together 
and are connected to one ball, d, of a spark gap. The other ball, 
d, is connected to the earth. From d and d wires c' c' are carried 
to an induction coil c. The 
primary of the coil with 
key 6 is in circuit with a 
battery a. On depressing 
the key, an oscillatory 
discharge takes place 
across the gap, and by 
charging and discharging 
affects the whole length of 
the vertical wire. Ether 

waves go off from the wire through space, with a general tend- 
ency to follow the curvature of the earth. They travel best over 
water, so that the ocean is peculiarly adapted for the use of 
wireless telegraphy. 

Marconi, beginning with vertical wires only twenty feet long, 
sent signals a mile. He found that increasing the length of the 
wire increased the distance of transmission, and the rule of the 
distance varying with the square of the length of the wire was 
at one time suggested, but has been abandoned. 

Receiving Apparatus. — At the distant receiving station the 
system of antennae is established, whose lower end is grounded 
with the primary of an induction coil in series. The secondary 
of the induction coil is in series with a battery and relay mag- 
net. In parallel with the battery and relay magnet is the 
coherer. 



■^IJh 



Fig. 554. 



-Principle of Tbansmitiing 
Apparatus. 



734! 



ELECTRICIANS' HANDY BOOK, 



Connection of Stations.— Referring to Fig. 555, 1 is the trans- 
mitting station with its antenna Ai, spark gap & &, induction 
coil secondary S^ and primary P^, sending key K, and battery B^. 
On working the key, sparks pass between h and 6, affecting the 
antennae. Ether waves fly through space and are caught by 
the antennae A^ of the receiving station 2. The disturbance 
sends a momentary current through the primary Pg of the in- 
duction coil. Its secondary S2 then sends a current through 




Fig. 555.— WiBEiiEss Telegraphy Connections. 



the coherer c. This reduces the resistance of the coherer, and 
a current goes through it due to the battery B2 and through the 
relay magnet R, operating a Morse receiver on local circuit. 

There is a hammer which actuated by an electric magnet 
and make and break constantly taps the coherer, so that the 
coherer only retains its conductivity while acted on by ether 
waves. The instant they cease, the tapping restores its resist- 
ance. Long and short signals for the Morse code are sent by 
holding down the key K at the transmitting station for long 
or short periods. They are received by the receiving station and 
printed on a tape. 



>'' 



WIRELESS TELEGRAPHY. 735 

Antennae and Connections. — Wires as nearly vertical as the 
requirements of suspension apparatus permit are used both for 
transmitting and receiving. The following may be given as a ty- 
pical example of the installation of such wires: Four iron lattice 
masts, each about 220 feet high, have their upper ends con- 
nected by horizontal wires, whence a quantity of small copper 
wires lead to the center of the system on the ground. Horizontal 
wires are without effect. The copper wires represent in appear- 
ance a sort of funnel. Such stations have been established on 
Cape Cod, U. S. A., and elsewhere on the coast. There is noth- 
ing final about this arrangement. At Poldhu, England, twenty 
masts are arranged in a circle to sustain the wires. Four hun- 
dred bare copper wires, each wire 200 feet long, are used. 




Fig. 556.— Marconi's Coherer. 

The wires are all connected at their lower ends to one terminal 
of a coil of a special induction coil. The other terminal of the 
coil is connected to the earth. From the secondary terminals 
of the coil wires are taken to condensers, whose other terminals 
are connected to the secondary of an induction coil. A con- 
denser is placed in this circuit, and across it and in parallel 
with the secondary coils is a spark gap connection. This gen- 
erally carries a pair of balls. The primary of the last-named 
induction coil receives current from a dynamo or storage bat- 
tery, and current is given or taken off by a sounding key. 

For ships two antenna are used. Near the mast top a yard 
about 30 feet long is slung, and from its ends two copper wire 
ropes about y^ inch in diameter are led down to the receiving 
and transmitting apparatus. Similar antennse are used for short- 
distance land stations. 



736 ELECTRICIANS' HANDY BOOK. 

Marconi's Coherers. — ^Marconi's coherer, shown in Fig. 556, 
is a tube 1% inches long and 1/12 inch internal diameter. A 
chamber is made in the center by introducing two silver plugs 
with their ends 1/30 inch^ apart. A mixture of 90 per cent 
nickel filings and 10 per cent silver filings is contained in this 
space with a minute quantity of mercury. 

Hysteresis and Other Receivers. — The coherer used as a re- 
ceiver operates a relay circuit, and prints the message on a tape 
in Morse characters or their equivalent. This has the advan- 
tage of giving a fixed record. There are a number of receivers 
which do not give a record, some of which are based on magnetic 
lag. The hysteresis of iron is modified by ether waves impinging 
on it. In one of Marconi's receivers an endless iron wire is 
stretched around two pulleys, and passes through the core or axis 
of a double coil of insulated wire. The arrangement represents 
^n induction coil with moving core. The primary receives the 
Impulses from the receiving antennae as already described. The 
secondary connects with a telephone receiver. The impulses modi- 
fy the hysteresis of the moving core, and sound is produced in 
the telephone. In another construction the core of the induction 
coil is fixed, and an electro-magnet rotates in front of it. The 
ether waves modify the hysteresis as in the case just cited, and 
the message is received by a telephone. 

There are a number of other constructions of receiving instru- 
ments in which a telephone is used as a receiver, the great sen- 
sitiveness of the telephone receiver causing them to be operative. 
The action of the ether waves on these classes of instruments is 
so slight that the instruments can only be used with a telephone 
receiver, and cannot actuate a printing recorder. On the other 
hand, the acoustic instruments are faster, other things being equal. 



INDEX. 



Access of Air 439 

Accidents to Motors 415 

Acid Depolarizers, Sulpliuric 

and jSitric 110 

Acid Storage Batteries, Zinc. . 140 

Action of a Circuit 66 

Action of Arc Lamp on Con- 
stant-Potential Circuit 553 

Action of a Storage Battery. 125 

Action of Conductor 51 

Action of Current on the jNIag- 

net 202 

Action of Currents, Mutual . . . 199 
Action of Drum Armature .... 233 

Action of Inclosed-Arc 546 

Action of Magnet Poles on 

Each Other 195 

Adjusting Lamps 559 

Adjusting Weight 552 

Adjustment, Clutch Stop 560 

Air-Blast Cooling 386 

Air Blast, Effect of 538 

Air Gap and Sparking 310 

Air Pump, The Mercury 528 

Air Switches 447 

Air-Vane Damping 461 

Alarm, Ground 457 

Alternating-Current Arc 544 

Alternating - Current Arc 

Lamps, Distribution of Light 

of 544 

Alternating - Current Arc 

Lamps. Efficiency of 545 

Alternating-Current Arc, Pow- 
er-Factor in 544 

Alternating-Current Armature 

Winding. Principle of 350 

Alternating- Current Circuit, 
Counter and Forward E.M.F. 

in 334 

Alternating - Current Circuit, 

E.M.F. in 333 

Alternating Current, Direct 

Current from 390 

Alternating Current Distribu- 
tion 504 

Alternating-Current Dynamo, 

Elementary Idea of 219 

Alternating Current, Genera- 
tion of 348 

Alternating-Current Ground In- 
dicator 456 

^Alternating-Current Lightning 

Arrester, Low-Equivalent. . . 521 
Alternating-Current Potential 

Regulator 454 

Alternating Current, Y. Connec- 
tions for 506 

Alternating E.M.F 316 



AlternatiPg E.M.F, and Cur- 
rent, Cause of Form of 319 

Alternating E.M.F. and Cur- 
rent Curves 320 

Alternating E.M.F. and Cur- 
rent, F'orm of 318 

Alternating E.M.F. and Cur- 
rent, Production of 318 

Alternating Quantities, Multi- 
plication of 344 

Alternating Quantities, Sum- 
mation of 342 

Alternator Brushes 435 

Alternator, Inductor 356 

Alternators, Field Magnets of 436 

Alternators in Step 405 

Alternators, Trouble in Rotors 

of 435 

Alternator Winding, Six-Wire 

Connection of Three-Phase. 359 
Aluminium Negative Plate.... 101 
Amalgamation of Primary Bat- 
tery 96 

American Storage Battery. . . . 134 

American Wire Gauge 85 

Ammeters 467 

Ammeter, Shunted 469 

Ammeter, Total-Current Sole- 
noid 467 

Ammeter, Transformer 470 

Ammonium-Chloride Batteries. 119 

Ampere, Analogy for the 53 

Amperes and Coulombs, Cur- 
rent 52 

Ampere's Rule 203 

Ampere's Paile Adapted to In- 
duction 213 

Ampere's Theory of Magnetism 200 
Ampere's Theory of Terrestrial 

Magnetism 201 

Ampere Turns 176 

Ampere Turns and Lines of 

Force, Relation between.... 183 
Analogies of Drop of Poten- 
tial 60 

Analogy for the Ampere 53 

Angular Measurement 32 

Annealing 181 

Annunciator Lamp. Telephone. 709 
Annunciator, The Mechanical. 708 
Annular Chambered Magnet. . . 191 

Anodes 660 

Anode and Cathode, Position of 670 
Anten le and Connections.... 735 

Anti-Pci-allel Systems 488 

Apparanjs, Large Plating. . . . 661 

Appara<-us, "Photometer 567 

Appa^ is. Receiving, Tele- 
phone 733 



(37 



738 



ELECTRICIANS' HANDY BOOK. 



Apparatus, Simple Plating. . . . 661 
Apparatus, Transmitting, Tele- 
phone 733 

Appliances and Generators in 

Circuits 65 

Appliances, Circuits without. . 64 
Application of Circular Mil 

System 84 

Application of Lenz's Law... 214 

Arc, Alternating-Current 544 

Arc and Incandescent Lamp 

Circuits 472 

Arc Blowpipe, The Electric... 727 

Arc. The Direct-Current Open. 540 
Arc, Direct Heating by the 

Electric 727 

Arc, Distribution of Light in 

Direct-Current Open 541 

Arc, Heat of 536 

Arc, Hissing 543 

Arc Lamp, Direct Photometer- 

ing of 572 

Arc Lamps, Features of Series 
or Constant-Current System 

for 475 

Arc Lamp on Constant-Poten- 
tial Circuit, Action of 553 

Arc Lamp, Photometry of . . . . 576 

Arc Lamp, Resistance Coil in. 553 
Arc Lamps, Commercial Rating 

of 542 

Arc Lamps, Constant-Current 

or Series 551 

Arc Lamps, Constant-Potential 555 
Arc Lamps, Distribution of 

Light of Alternating-Current 544 
Arc Lamps, Efficiency of Alter- 
nating-Current 545 

Arc Lamps, Noise in 545 

Arc, Length of 545 

Arc Length, Voltage Drop and 538 
Arc Light, Candle-Power in, 

Watts per 579 

Arc Light Carbons 539 

Arc Light, Efficiency of 537 

Are Light. Quality of -. . . 580 

Arc Lights, Distribution of 

Light from 582 

Arc, Power Consumed in 538 

Arc, Power-Factor in Alternat- 
ing-Current 544 

Arc Proper, Ligbt Given by. . 543 

Arc Proper, Resistance of . . . . 537 

Arc, Striking the 535 

Arc, The Voltaic 535 

Arcs, Resistance of Longer... 543 
Arcs, Resistance of Short.... 543 
Area of a Circular Mil, Exam- 
ples of 84 

Arithmetic and Mathematics. 17-40 

Armature, Action of Drum... 233 

Armature and Core 221 

Armature, Balancing of 428 

Armature out of Center 429 



Armature, Centering of 

Armature, Closed-Coil Direct- 
Current 

Armature, Commutator Connec- 
tions of Ring 

Armature Connections, Drum. 

Armature Core, Action of 
Field Poles on 

Armature Core, Increasing 
B.M.F. by Adding 

Armature Cores, Eddy Cur- 
rents in 

Armature, Current in Ring. . . 

Armature, Disk 

Armature, The Drum 

Armature, End Leakage of 
Lines of Force in 

Armature, Mounting of Ring. . 

Armature, Multipolar Ring. . . 

Armature, Open-Wound Four- 
Part Ring 

Armature, The Pacinotti 

Armature, Pole Single-Phase . . 

Armature Polarity Due to 
Windings 

Armature Reaction Diagrams. 

Armature in Rotary Field.... 

Armature Rotation, Reversal of 

Armature Running 

Armature Shaft, End Motion in 

Armature, Short Circuits in . . 

Armature, Single-Phase 

Armature, Sixteen-Conductor 
Bipolar 

Armature, 

Armature, 

Armature 



Squirrel Cage 

Spindle or H 

Winding, General 
Formulas for Drum 

Armature Winding, Nomencla- 
ture for Drum 

Armature Winding, Principle 
of Alternating-Current .... 

Armature Windings, Break in. 

Armature Windings. Drum . . . 

Armature Windings and Frame, 
Short Circuits between 

Armature, Winding a Drum . . 

Armature Winding, Simple Sys- 
em of . 

Armature Windings, Laying out 
Drum 

Armatures, Cores of Ring. . . . 

Armatures, Modern Types of 
Closed-Coil 

Armatures, Open Coil. . 

Armatures, Pole 

Armatures, Various 

Armatures ■with F'ormed Coil, 
Winding . 

Arrangements of Batterips. . . . 

Arrester, Comb or Saw-Tooth, 
Lightnina- 

Arrester, Discriminating Light- 
ning . , 



428 

223 

227 
350 

265 

221 

271 
229 
303 
281 

272 
230 
231 

230 

225 
354 

265 
266 
364 
404 
428 
423 
423 
348 

035 

.367 
000 



246 

246 

350 
422 
233 

435 
241 

234 

243 

228 

226 
222 
301 
193 



» 



301 
122 

518 

519 



INDEX. 



739 



Arrester, Double-Pole Light- 
ning 522 

Arrester, Liglitning 591 

Arrester, Low-Equivalent Alter- 
nating-Current Lightning... 521 
Arrester. Magnetic Blow-Out, 

Lightning 518 

Arrester, Non-Arcing Metal, 

Lightning 510 

Arrester, Tank Lightning 522 

Arrester, Westinghouse Light- 
ning 521 

Arrival Curve 54 

Astatic Galvanometer 605 

Atomic Weights and Chemical 

Equivalents 89 

Attraction and Repulsion of 

Magnetic Poles 202 

Automatic Cut-Out 150 

Automatic Regulation of Volt- 
age ^. 492 

Auto-Transformer, The 381 

Auxiliary Feeder Connections. 495 
Average Values 327 

S and E Curves 178 

B and H Curves, Interpreta- 
tion of 179 

B and H Synonyms for 178 

Backing Up Deposits 675 

Ballistic Calculation 614 

Ballistic Galvanometer, The.. 610 

Ballistic Measurement 613 

Bar, Calculating Scale of Pho- 
tometer 568 

Bar Photometer 563 

Bath, Placing Molds in 674 

Baths, Temperature of Plating 671 

Battery, Action of a Storage. 125 
Battery, Amalgamation of 

Primary 96 

Battery. American Storage. . . . 134 

Battery, Baudet Siphon 107 

Battery, Bunsen's 103 

Battery, Camacho Cascade... 107 

Battery Cell. The Primary... 93 
Battery Cells, Insulation of 

Storage 161 

Battery Cells, Storage 161 

Battery, The Charge of Stor- 
age 145 

Battery, Charging Storage.... 166 

Battery, Chloride 136 

Battery Connections, Booster 

and Storage 410 

Battery Connections, Making 

Storage 161 

Battery, Crompton-Howell . . . . 135 

Battery, The Daniell Ill 

Battery, Depolarizing Mixtures 

in Poggendoi-ff 109 

Battery, Determination of Dis- 
charge of Storage 145 



Battery, E'dison's Storage 140 

Battery, End Cells of Storage 164 

Battery, E.P.S 135 

Battery Equalizer in Three- 
Wire System, Storage 501 

Battery, Exciting Solutions in 

PoggendorfiE 109 

Battery, Exhaustion of Pri- 
mary 96 

Battery, Faure's 130 

Battery, The Faure-Sellon- 

Volckmar 131 

Battery, Floating Storage. 166, 410 
Battery, Fuller's Mercury-Bi- 
chromate 106 

Battery, Function of a Storage 128 

Battery, Gibhs' 105 

Battery, Gould Storage 132 

Battery, Gravity 114 

Battery, Grenet's 108 

Battery, Grove's 102 

Battery, Grove's Gas 126 

Battery, Helios-Upton 133 

Battery, Local Action of Pri- 
mary 96 

Battery, Meidinger's 114 

Battery, Modifications of Bun- 
sen's 104 

Battery, Modifications of Dan- 

iell's 112 

Battery, Modifications of La- 

lande and Chaperon 119 

Battery, Modifications of Pog- 

gendorff's 106 

Battery, Nomenclature of Pri- 
mary 95 

Battery on Open Circuit, Dis- 
charge of Storage 144 

Battery, Parts of Primary. ... 93 

Battery, Partz's 109 

Battery, Plante's 128 

Battery, Poggendorff's 105 

Battery, Polarization of Pri- 
mary 96 

Battery, Radiguet 108 

Battery, Requirements of a 

Storage 128 

Battery, Sand Type of Dan- 

iell's . , 114 

Battery out of Service, Tak- 
ing Storage 160 

Battery, Setting up a Storage 153 

Battery, Smee's 103 

Battery System, Dean's Com- 
mon 698 

Batteiy System, Stone's Com- 
mon 698 

Battery Systems, Common. . . . 697 

Battery, Tudor 138 

Battery, Wadell-Entz 140 

Battery, Wollaston's 99 

Batteries, Ammonium-Chloride 119 

Batteries, Arrangements of... 122 

Batteries, Caustic Alkali 117 



740 



ELECTRICIANS' HANDY BOOK. 



Batteries, Chemical Action of 

Storage 131 

Batteries, Copper Storage.... 139 

Batteries, Dip ^ 108 

Batteries, Dry 121 

Batteries, Forming Storage... 129 
Batteries in Three-Wire Sys- 
tem, Storage 500 

Batteries, Manufacturer's Data 

with Storage 144 

Batteries, Modern 100 

Batteries, Notes on Storage... 163 
Batteries, Resistance of Stor- 
age 132 

Batteries, Simple 93 

Batteries, Zinc-Acid Storage.. 140 

Baudet Siphon Battery 107 

Bell, Polarized 691 

Bell Wiring 718 

Bells for Party Lines, Polar- 
ized 700 

Bichromate Solutions, Potas- 
sium 110 

Binding Posts 441 

Bipolar Armature, Sixteen-Con- 

ductor 235 

Bipolar Armature, Twelve- 
Conductor 235 

Bipolar Field, Double-Layer 

Winding for 244 

Bipolar F'ield, Single Layer 

Winding for 243 

Bipolar Winding Formulas... 247 

Blake Transmitter, The 680 

Blow-Out Lightning Arrester, 

Magnetic • 518 

Blow-Out Magnet 596 

Blowpipe, The Electric Arc... 727 

Board and Cut-Outs 596 

Boards, Distributing 703 

Booster and Storage Battery 

Connections 410 

Booster, Automatic 408 

Booster Connections 406, 408 

Booster, Hand Regulation of . .,407 

Booster, Motor and 501 

Boosters, Motor-Dynamos as.. 408 

Boosters. Regulators or 406 

Bouguer's Photometer 570 

Bracket Telephones, Induction 

Coils in 688 

Brake. Excessive Use of in 

Trollev 597 

Brake. Prony. The 38 

Branly's Coherer 732 

Breaker. Circuit 150 

Break in Armature Windings. 422 

Break in Field Winding 430 

Bridged Telephone Circuit. . . . 696 

Bridge Key 635 

Bridge, Operation of Wheat- 
stone 634 

Bridge or Bridge Box, Wheat- 
stone 632 



Bridge, The Meter 634 

Bridge, Wheatstone 632 

British Association Standard 

Ohm 627 

Brush Adi'ustment 268 

Brush Holders 305 

Brush Pressure 420 

Brush Rigging 309 

Brushes 220, 305 

Brushes, Alternator 435 

Brushes and Brush Holders. . 420 

Brushes, Carbon 421 

Brushes, Copper 421 

Brushes, Hard Carbon 422 

Brushes, Lifting 422 

Brushes, Position of 421 

Brushes, Position of Opposite. 309 

Brushes, Replacing and Setting 421 

Brushes. Tangential 306 

Brushes. Trimming Metal 307 

Buckling of Plates 153 

Building up the Field of Force 173 

Bunsen's Battery 103 

Bunsen's Battery, Modifications 

of 104 

Bunsen's Photometer Disk. . . . 564 

Bus-Bar, Transfer 495 

Cable and Line Tests, Galvano- 

scope ..." 650 

Cable, Determination of Capa- 
city of 648 

Cable, Finding Wire Ends in. . 653 
Cable, Insulation Resistance 

of 646 

Cable, Making Branch Connec- 
tion in 653 

Cable on Reels, Tests of 652 

Cadmium Plate 156 

Calculation, Ballistic 614 

Calculation, Example of Com- 
pound Winding 259 

Calculation, Example of Coun- 
ter E.M.F. Drop 82 

Calculation for Conical Con- 
ductor 486 

Calculation of Resistance of 

Parallel Circuits 81 

Calculations, Electrical 17 

Calculations, Examples of R.I. 

Drop 82 

Calculations for Series Distri- 
bution 475 

Calculations, Voltage 92 

Calibration 524 

Calorimeter. Hare's 99 

Camacho Cascade Battery.... 107 

Candle, .Jablochkoff 561 

Candle, Standard, English.... 567* 
Candle-Power in Arc Light, m 

Watts per 579j 

Candle-Power in Incandescent fl 

Lamps, Watts per 580H 



INDEX. 



741 



Candle-Power of Incandescent 

Lamps 576 

Candle-Power, Spherical 574 

Capacity 47, 388 

Capacity, Composition of Re- 
sistance,. Inductance, and. . 343 

Capacity, Examples of 49 

Capacity of Cable, Determina- 
tion of 648 

Capacity of Condensers 44 

Capacity, Ohmic Equivalent of 

Reactance of 337 

Capacity, Reactance of 338 

Capacity, Specific Inductive. . . 48 

Capacity, Storage 130 

Carboning a Lamp 561 

Carbonization 524 

Carbon-Feed Lamps 549 

Carbon Holder, Globe and 547 

Carbon Holders 550 

Carbon Negative Plates 103 

Carbon Transmitters, Loose. . . 681 

Carbons, Arc Light 539 

Carbons, Duration of 545 

Carbons, Inclosed-Arc . 547, 559, 560 
Carbons, Positive and Nega- 
tive 535, 560 

Carbons, Quality of 538 

Carbons, Wearing of 539 

Cardew Voltmeter 463 

Car, Economical Running of. 597 

Car, Jerking 601 

Car Heating 601 

Car, Leaving the 598 

Car Motor, Construction of . . . 588 
Car Motors, Horse-Power of.. 586 

Car, Reversing the 598 

Cascade Battery. Camacho. . . . 107 
Cathode, Position of Anode and 670 

Causes of Lag and Lead 341 

Cell 96 

Cell, Modification of Gravity. 116 

Cell, The Primary Battery 93 

Cells, Counter, E.M.F 165 

Cells, Insulation of Storage 

Battery 161 

Cells of Storage Battery, End 164 
Cells, Short-Circuiting of Sin- 
gle 152 

Cells, Storage Battery 161 

Center, Armature out of 429 

Centering of Armature 428 

Change, Graphic Representa- 
tion of Rate of 323 

Change, Rate of 323 

Changing Voltage 400 

Characteristic Curves. See 

Curves. Characteristic. 
Charge, E.M.F. and the Static 58 

Charge, First 150 

Charge of Storage Battery, 

The ■. 145 

Charging 43 

Charging, English Rule for... 151 



Charging from Lighting Cir- 
cuits, Connections for 157 

Charging Storage Battery.,,. 166 
Chemical Action of Storage 

Batteries 131 

Chemical Decomposition, Cur- 
rent Strength and 90 

Chemical Decomposition, E.M. 

F. in 91 

Chemical Decomposition, En- 
ergy in 91 

Chemical Equivalents, Atomic 

Weights and, 89 

Chloride Battery 136 

Choke Coils 505 

Choking of Transformer 376 

Circle, Generating 322 

Circle, Interpretation of the 

Generating 323 

Circuit, Action of a 66 

Circuit and Inductance, Turns 

of a 334 

Circuit, Action of Arc Lamp on 

Constant Potential 553 

Circuit-Breaker 150 

Circuit-Breaker, Magnetic Re- 
lease Underload 453 

Circuit-Breaker, Mechanical Re- 
lease LTnderload 453 

Circuit-Breaker, Reverse Cur- 
rent 454 

Circuit-Brealier, Switch Boxes 

and, on Car. 590 

Circuit-Breakers as Switches.. 454 
Circuit-Breakers, Combined . . 454 
Circuit-Breakers, Overload. . . . 451 
Circuit-Breakers, Underload.. 452 
Circuit, Bridged Telephone... 696 

Circuit, Condensers in a 64 

Circuit, Constant Current .... 78 
Circuit, Constant Potential... 78 
Circuit, Constitution of a ... . 63 
Circuit, Counter and F'orward 
E.M.F. in Alternating-Cur- 
rent 334 

Circuit, Discharge of Storage 

Battery on Open 144 

Circuit, E.M.F. in Alternating- 
Current 333 

Circuit, Energy and the Mag- 
netic 172 

Circuit, Exciting Series Coils 

from Main 261 

Circuit, Nature of the Mag- 
netic 174 

Circuit, Outer 68 

Circuit, Permeance of a Mag- 
netic 184 

Circuit. Polarity of the 159 

Circuit, Qualities of a 331 

Circuit, Series Telephone 695 

Circuit, Short 69 

Circuit, Short Circuits in Out- 
er 432 



742 



ELECTRICIANS' HANDY BOOK. 



Circuit, The Electric 63 

Circuit, Tlie Magnetic 172 

Circuit, Tliree Elements in a . 74 
Circuit, Ttiree Factors of Mag- 
netic 175 

Circuit without Resistance . . 71 
Circuits. Arc and Incandes- 
cent Lamp 472 

Circuits, Appliances and Gene- 
rators in . . i 65 

Circuits, Calculation of Resist- 
ance of Parallel 81 

Circuits, Connections for 

Charging from Lighting.... 157 

Circuits, Independent 492 

Circuits, Open and Closed.... 64 

Circuits without Appliances. . 64 

Circular Developments 238 

Circular Functions, Numerical 

Value of 34 

Circular Mil, Area of 84 

Circular Mil System 83 

Circular Mil System, Applica- 
tion of 84 

Classification 483 

Clerk Maxwell's Rule 213 

Closed Circuits, Open and.... 64 
Closed-Coil Armatures, Modern 

Types of 226 

Closed - Coil Direct - Current 

Armature 223 

Closet System 484 

Clouds, E.M.F. in Thunder... 58 

Clutch. The 548 

Clutch Stop Adjustment 560 

Coherer, Branly's 732 

Coherer, Marconi's 736 

Coil and Electro-Magnet, Mag- 
netizing by 197 

Coil, Damping 460 

Coil. Dimensions of Telephone 

Induction 686 

Coil, Disconnecting or Open- 
ing Shunt 260 

Coil. Efeect of Independent Ex- 
citation of Shunt 260 

Coil, Effect of Telephone In- 
duction 688 

Coils, Arrangement of Resist- 
ance 627 

Coils, Choke 505 

Coils. Direction of Current In- 
duced in 217 

Coils from Main Circuit, Excit- 
ing Series 261 

Coils, Heating of Field 429 

Coils in Arc Lamp Resistance. 553 
Coils in Bracket Telephones, 

Induction 688 

Coils in Comnound Dynamos, 

Excitation of Field 260 

Coils. Modern Arrangements of 

Resistance , 6'^8 

Coils, Pancake 381 



Coils, Practical Notes on Re- 
sistance 631 

Coils, Proportional 636 

Coils, Reactance or Economy. 545 

Coils, Repeating 705 

Coils, Resistance 626 

Coils, Resistance, Spools for.. 631 
Coils, Separate Excitation of 

Shunt 261 

Coils, Telephone Induction . . . 684 
Coils, Winding Armatures with 

Formed 301 

Collecting or Slip Rings . . 219 

Collector Rings 419 

Colors, Distinguishing, of 

Wires 722 

Commercial Rating of Arc 

Lamps 542 

Commutator Bars. Bad Con- 
tacts between Winding and. 419 

Commutator Bars, Loose 420 

Commutator Connections. .238, 245 
Commutator Connections, De- 
velopment of 240 

Commutator Connections of 

Ring Armature 227 

Commutator Construction 303 

Commutator, Filing 433 

Commutator, Material of .... 419 

Commutator, Oval 420 

Commutator, Position of 305 

Commutator, Sandnanering. . . 483 
Commutator, Smoothing .... 433 

Commutator, Sparking 'of 424 

Commutator Surface, Gummy 

or Sticky 420 

Commutator Surface, Lubricat- 
ing 420 

Commutator, Temperature of.. 419 
Commutator. Turning down. . . 432 

Compensated Voltmeter 470 

Compensating Resistance 619 

Compensator. Inductance .... 471 

Compensator, Ohmic 471 

Compensator, Starting 368 

Compensators 409, 470 

Composition of Resistance, In- 
ductance and Capacity 343 

Compound Dvnamos, Excita- 
tion of Field Coils in 260 

Compound Dynamos, Parallel 

Coupling of 402 

Compound Dynamo. Wrong 

Connections in 432 

Compound Winding 256 

Compound Winding Calcula- 
tion. Examnle of 259 

Compound Winding, Long- 
Shunt 256 

Compound Winding. Short- 
Shunt 256 

Compound Wound Dynamos, 

Self-Resrulation of 257 

Compounding, Over- 259 



INDEX. 



743 



Concentric Magnets in Lamps. 550 

Condenser, Earthing a 44 

Condenser, Single Surface 45 

Condensers 42 

Condensers; Capacity of 44 

Condensers in a Circuit 64 

Conditions for Inducing Elec- 
tric Energy 20G 

Conditions of Sensitiveness... 636 

Conductance 69 

Conductance and Cross-Sec- 

lional Area of Conductors.. 8.3 

Conductibilitv 69 

Conduction, Electrolytic 73 

Conduction Interference 714 

Conductivity 69 

Conductor, Action of a 51 

Conductor, Calculation for 

Conical 486 

Conductor in a Field of Force, 

Motion of 169 

Conductor, Inductance React- 
ance in Subdivided 336 

Conductor, Lines of Force Pro- 
duced by a Curved 169 

Conductors, Conductance and 

Cross-Sectional Area of . . . . 83 
Conductors, Cylindrical and 

Conical 485 

Conductors, Eddy Currents in. 272 

Conductors, Electrolytic 66 

Conductors and Non-Conduc- 

tors 50 

Conductors, Size of, for Plat- 
ing 669 

Conical Conductor, Calculation 

for 486 

Conical Conductors, Cylindri- 
cal and 485 

Connection, Delta or Mesh. 361, 507 
Connection in Cable, Making 

Branch 653 

Connection of Stations 734 

Connection, Y or Star 359 

Connections. Antennae and, in 

Wireless Telegraphy 735 

Connections. Auxiliary Feeder 495 

Connections, Booster 406 

Connections. Booster and Stor- 
age Battery 410 

Connections, Commutator .238, 245 
Connections, Development of 

Commutator 240 

Connections, Drum Armature. 350 
Connections, Examining, on 

Cars 599 

Connections for Alternating- 
Current, Y 506 

Connections for Charging from 

Lighting Circuits 157 

Connections in Compound 

Dynamos, Wrong 432 

Connections, Making Storage 

Battery • 161 



Connections, Line 362 

Connections, Multipolar Dyna- 
mo 264 

Connections of Ring Armature, 

Commutator 227 

Connections, Switchboard .... 712 
Conservation of Electricity.... 57 

Constancy of Magnetism 199 

Constant-Current Circuit 78 

Constant-Current or Series Arc 

Lamps 551 

Constant-Current System 472 

Constant-Current System for 
Arc Lamps, Features of 

Series or ..." 475 

Constant-Current Transform- 
ers T 387 

Constant, Determination of the 620 

Constant, Hysteretic 186 

Constant of Galvanometer.... 620 
Constant-Potential Arc Lamps 555 

Constant- Potential Circuit 78 

Constant-Potential Systems... 473 

Constants. Useful 35 

Constitution of a Circuit 63 

Contacts between Winding and 

Commutator Bars, Bad 419 

Control, Crocker- Wheeler Speed 414 

Controller Points 593 

Controller, Rheostat 596 

Controller, Series-Parallel . . . 594 
Controller Troubles on Cars.. 600 

Controllers 592 

Construction, Advantages of 

Multipolar 252 

Construction, Multipolar 350 

Conventional Representations 

of Machines 264 

Converter, Functions of a Ro- 
tary 394 

Converter in Three-Wire Sys- 
tem, Rotary 393 

Converter, Rotary 390 

Converter, Starting a Rotary.. 394 
Cooking and Domestic Heat- 
ing. Electric 728 

Cooking, Power Required for. 723 

Cooling, Air-BIast 386 

Cooling, Oil 384 

Cooling, Water 385 

Copper Loss, The 584 

Copper-Plating 662 

Copper, Saving in 497 

Copper Storage Batteries 139 

Core, Action of Field Poles on 

Armature 265 

Core, Armature and 221 

Core Grooves 301 

Core, Increasing E. M. F. by 

Adding Armature 221 

Core, Permeance of Ring 228 

Core Transformers 380 

Cores, Eddy Currents in Arma- 
ture 271 



744 



ELECTRICIANS' HANDY BOOK. 



Cores of Ring Armatures ..... 228 

Cotton Waste 439 

Coulomb, Hydrogen Liberated 

by tlie 88 

Coulomb, Water Decomposed 

by the 88 

Coulombs, Current, Amperes 

and 52 

Counter Electromotive Force. 
See Counter E. M. F. 

Counter E. M. F 333, 536 

Counter and Forward E. M. F. 173 
Counter and Forward E. M. F. 
in Alternating-Current Cir- 
cuit 334 

Counter E. M. F. Cells 165 

Counter E. M. F., R. I. Drop 

and 79 

Counter E. M. F., Drop Cal- 
culation, Example of 82 

Couple 96 

Coupling of Compound Dyna- 
mos, Parallel 402 

Coupling of Shunt Dynamos, 

Parallel 402 

Critical Point of Shunt- 
Wound Dynamo 281 

Crocker-Wheeler Speed Con- 
trol 414 

Crompton-Howell Battery . . . 135 

Crushers 413 

Current from Alternating Cur- 
rent, Direct 390 

Current, Amperes and Coul- 
ombs 52 

Current and Rate Units. ..... 50 

Current Armature, Closed-Coil 

Direct . . 223 

Current, Cause of Form of 

Alternating E. M. F. and.. 319 
Current Circuit, Constant.... 78 

Current, Critical 279 

Current Curves, Alternating 

E. M. F. and 320 

Current Curves, Drawing B. M. 

F. and 321 

Current Curve. E. M. F. and. 316 

Current, Direction of a 55 

Current Distribution, Alternat- 
ing 504 

Current Dynamo, Elementary 

Idea of Alternating 219 

Current Dynamo, Pllementary 

Idea of Direct . 220 

Current in Electroplating, 

Regulation of 661 

Cur-rent for Electroplating. . . 660 

Current, Ether and 167 

Current, Fields of Force and 

Lines of Force Due to. . . . 55 
Current, Form of Alternating 

E. M. F. and 318 

Current, Generation of Alter- 

natinsr 348 



Current, Induced, Develop- 
ment of 240 

Current Induced in Coils, Di- 
rection of 217 

Current Intensity in Plating. . 669 
Current Measurement with 

Potentiometer 640 

Current on the Magnet, Ac- 
tion of a 202 

Current, Production of 52 

Current. Production of Alter- 
nating E. M. F. and 318 

Current in Rotary Transform- 
er, Relations of Voltage and 392 
Current, Reversing Direction 

of 416 

Current, Speed of a 54 

Current, Standard Series 

Lighting 477 

Current Strength 53 

Current Strength and Chemi- 
cal Decomposition . 90 

Current, Three-Phase 347 

Current, Time Required to Pro- 
duce a 52 

Current to Drop, Relation of. 491 

Current, Two-Phase 346 

Current, Wattless 246 

Current, Y Connections for 

Alternating 506 

Currents in Armature Cores, 

Eddy 271 

Currents in Conductors, Eddy. 272 
Currents in Core Disks. Eddy. 271 
Currents, Fbucault or Eddy. 

215, 271, 429 
Currents, Mutual Action of. . 199 
Currents in Pole Pieces, Eddy. 272 

Curve, Arrival 54 

Curve, Droopins? Characteristic 275 
Curve, E. M. F'. and Current. 316 
Curve of Shunt Dynamo, Total 

Characteristic 203 

Curve, of Shunt Dynamo, Total 

Current Characteristic 282 

Curve, Sine 321 

Curve^. Vector Diagram of Sine 325 
Curved Co^nductor, Lines of 

Force Produced by a 169 

Curves, Alternating E'. M. F. 

and Current 320 

Curves, B and H 178 

Curves, Characteristic.258, 273, 276 
Curves, Determination of .... 182 
Curves, Drawing Character- 
istic 277, 321 

Curves, General Notes on 

Characteristic 279 

Curves, Hysteresis 185 

Curves, Internal Characteristic. 277 
Curves, Interpretation of B 

and H 179 

Curves,- Interpretation of 
Characteristic 276 



INDEX. 



745 



Curves, Ohm-Volt 284 

Curves, I'ermeability ISO 

Curves. Power 345 

Curves, Shunt-Wound Dynamo 

Characteristic 280 

Curves, Types of Character- 
istic 273 

Cutting Lines of Force, 

205, 209, 224 

Cut-Outs 560 

Cut-Out, Automatic 150 

Cut-Out, Film 478 

Cut-Outs, Board and 596 

Cut-Outs, Overload and ITnder- 

load 448 

Cycle 316 

Damping Air- Vane 461 

Damping Coil 460 

Daniell Battery Ill, 112 

Daniell Battery, Sand Type of 114 

Dash Pots 550 

Data with Storage Batteries, 

Manufacturer's 144 

Deflection, Direction of .... 637 

Degree System 321 

Delta or Mesh Connection. 361, 507 

Demagnetizing Turns 268 

Density, Field 176 

Density of a Field of Force. . 172 

Densities of Field. Varying. . 267 
Depolarizers, Sulphuric and 

Nitric Acid 110 

Depolarizing Mixtures in Pog- 

gendorff's Battery 109 

Deposits. Backing Up 675 

Deprez-D'Arsonval Galvanom- 
eter 611 

Detection of the Field of F'orce 168 

Determination of Curves.... 182 
Determination of Discharge of 

Storage Battery 145 

Dean's Common Battery Sys- 
tem 698 

Decade Plan. The 629 

Decomposition, Current 

Strength and Chemical .... 90 
Decomposition, E. M. F. in 

Chemical 91 

Decomposition, Energy in 

Chemical 91 

Developments, Circular 238 

Diagram of Sine Curve, Vector 325 

Diagrams, Armature Reaction. 266 

Dielectrics 48 

Difference of Potential, E. M. 

F. and 61 

Diffractive Photometer 574 

Dimensions of Telephone In- 
duction Coil , . 686 

Dip Batteries 108 

Direct-Current Armature, 

Closed-Coil 223 



Direct-Current Dynamo, Ele- 
mentary Idea of 220 

Direct-Current from Alternat- 
ing Current 390 

Direct-Current Ground Indi- 
cator 456 

Direct-Current Motor and 

Torque 285 

Direct-Current Open Arc 540 

Direct-Current Open Arc, Dis- 
tribution of Light in 541 

Direction of Current Induced 

in Coils 217 

Direction of Current, Reversing 416 

Direction of Deflection 637 

Discharge of Storage Batteries 144 
Discharge of Storage Battery, 

Determination of 145 

Discharge of Storage Battery 

on Open Circuit 144 

Disconnecting or ' Opening 

Shunt Coil 260 

Disintegration of Storage Bat- 
tery 153 

Disk Armature 303 

Disk, Bunsen 564 

Disk, Leeson 565 

Disk Winding of Transform- 
ers 387 

Disk Windings 357 

Disk- Wound Transformers . . . 380 
Disks, Mounting Photometer. . 565 
Disks, Eddy Currents in Core. 271 

Distortion. Field 265 

Distributing Boards 703 

Distribution, Alternating-Cur- 
rent 504 

Distribution, Calculations for 

Se^'ies 475 

Distribution, Disadvantages of 

Parallel 482 

Distribution. Elementary Case 

of Parallel 482 

Distribution, Limitations of 

Series 474 

Distribution, Objections to 

Series 481 

Distribution of Light 534 

Distribution of Light of Alter- 
nating-Current Arc Lamps . . 544 
Distribution of Light from 

Arc Lights 582 

Distribution of Light in Di- 
rect-Current Open Arc .... 541 
Distribution of Light from In- 
candescent Lamps 583 

Distribution. Parallel 481 

Distribution, Series 472 

Driving Points ._, 593 

Drop and Arc Length, Volt- 
age 538 

Drop and Fall of Potential.. 79 
Drop Calculation, Example of 
Counter E. M. F 82 



746 



ELECTRICIANS' HANDY BOOK. 



Drop Calculations, Examples 

of R. 1 82 

Drop in Parallel System, Po- 
tential 482 

Drop of Potential 60 

Drop of Potential, Analogies 

of 60 

Drop, Relation of Current to. . 491 

Drop, Voltage 536 

Drum Armature 231 

Drum Armature, Action of . . . 233 
Drum Armature Connections . 350 
Drum Armature, Winding a. . 241 
Drum Armature Winding, Gen- 
eral Formulas for 246 

Drum Armature Winding, 

Nomenclature for 246 

Drum Armature Windings.233, 243 

Dry Batteries 121 

Duties, Motorman's 597 

Dynamic and Static Electri- 
city 56 

Dynamo, Action of Separately- 
Excited 262 

Dynamo and Motor, Inter- 
changeability of 218 

Dynamo and Motor, Reversibil- 
ity of 285 

Dynamo, Balancing 501 

Dynamo Characteristic Curves, 

Shunt-Wound 280 

Dynamo, Critical Point of 

Shunt- Wound 281 

Dynamo Connections, Multi- 
polar 264 

Dynamo- Electric Generators... 218 
Dynamo, Elementarv Idea of 

Alternating-Current 219 

Dynamo, Elementary Idea of 

Direct-Current . /. 220 

Dynamo Frames, Earthing . . 431 
Dynamo, Modern Multipolar.. 250 
Dynamo or Motor, Tempera- 
ture of 439 

Dynamo, Separate-Circuit . . . 263 
Dynamo, Starting a ....... 428 

Dynamo, Telephone Receiver, a 212 

Dynamo, Three-Brush 499 

Dynamo, Total Characteristic 

Curve of Shunt 283 

Dynamo. Total Current Char- 
acteristic Curve in Shunt. 282 
Dynamos as Boosters, Motor. 408 
Dynamos and Magnetos, Reg- 
ulation of Separately-Ex- 
cited 262 

Dynamos, Excitation of Field 

Coils in Compound 260 

Dynamos. Field Magnet for 

Multipolar 310 

Dynamos, Field Winding of. . 252 
Dynamos, Parallel Coupling of 402 
Dynamos, Self-Regulation of 
Compound-Wound 257 



Dynamos, Separately- and Self- 
Excited 263 

Dynamos, Series Winding of. 252 

Dynamos, Shunt Winding of. . 254 

Dynamos, Soft Steel in 181 

Dynamos, Varieties of 219 

Dynamos, Wrong Connections 

in Compound 432 

Dynamometer, The 39 

Dynamometer, Siemens's 622 

Economy Coil, Reactance or. . . 545 

Economy, Feeder 496 

Edison's Meter 513 

Edison's Storage Battery.... 140 

Edison's Telephone 682 

Eddy Currents, Foucault or, 

215, 271, 429 
Eddy Currents in Armature 

Cores 271 

Eddy Currents in Conductors. 272 

Eddy Currents in Core Disks. 271 

Eddy Currents in Pole Pieces. 272 

Effective Values 328 

Effective Values, Formulas for 330 
Efficiency of Alternating-Cur- 
rent Arc Lamps 545 

Efficiency of Arc Light 537 

Efficiency of Electric Heating 723 
Electric Arc, see Arc. 

Electric Circuit, The 63 

Electric-Car Motor, The 584 

Electric Cooking and Domestic 

Heating 723 

Electric Energy, Conditions for 

Inducing 206 

Electric Generators, Dynamo. 218 
Electric Heating. Economy of. 730 
Electricity. Conservation of . . 57 
Electricity, Dynamic and Static 56 
Electricity, Ether Waves Pro- 
duced by 50 

Electricity, Quantity of. Mean- 
ing of 44 

Electric Resonance 339 

Electric Quantity, Storage of. 41 

Electrodes, Moving 103 

Electro-Chemical Equivalents. 89 
Electro-Chemistry, Summary of 90 
Electrolyte and Tests, Impuri- 
ties in 155 

Electrolyte, Preparing the . . 155 
Electrolyte. Specific' Gravity 
Variation of Storage Bat- 
tery 146 

Electrolytic Conduction ...66, 73 

Electro-Magnet •• . . 188 

Electro-Magnet, Magnetizing 

by Coil and 197 

Electro-Magnet, Spiral 189 

Electro-Magnet, Tractive Force 

of the 188 

Electro-Magnets, U-Shaped.... 189 

Electro-Magnetic Induction . . 205 



INDEX. 



747 



Electro-Magnetic Tractive 
Power 192 

Electrometer, Thomson or 
Kelvin Absolute 617 

Electromotive Force. See E. 
M. F. 

Electromotive Force, Counter. 
See Counter E. M. F. 

Electroplating 659 

Electroplating, Current for... 660 

Electroplating, Energy Absorb- 
ed in 659 

Electroplating, General Prin- 
ciples of 659 

Electroplating, Regulation of 
Current in 661 

E. M. F 55 

E. M. F., Alternating 316 

E. M. F. in Alternating-Cur- 
rent Circuit 333 

E. M. F'. in Chemical Decompo- 
sition 91 

E. M. F. the Cause of Current 59 

E. M. F. and Current, Cause 
of F'orm of Alternating. . . . 319 

E. M. F. and Current Curves. 316 

E. M. F. and Current Curves, 
Alternating 320 

E. M. F. and Current Curves, 
Drawing 321 

E. M. F. and Current, Form 
of Alternating 318 

E. M. F. and Current, Produc- 
tion of Alternating 318 

B. M. F. and Difference of 
Potential 61 

E. M. F. Drop Calculation, 
Example of 82 

E. ]M. F'. and Energy 56 

E. M. F'. Forward 173 

E. M. F. by Increasing Turns, 
Increasing 221 

E. M. F. Increasing, by Adding 
Armature Core . 221 

E. M. F. and the Static 
Charge 58 

E. M. F., Counter. See Count- 
er E. M. F. 

E. M. F., Production of 56 

E. M. F. in Thunder Clouds . . 58 

E. M. F., Variations in Im- 
pressed 216 

End Cells of Storage Battery. 164 

End Motion in Armature Shaft 428 

Energy Absorbed in Electro- 
plating 659 

Energy in Chemical Decompo- 
sition 91 

Energy, Conditions for In- 
ducing Electric 206 

Energy Due to Hysteresis, 
Loss of 186 

Energy, B. M. F. and 56 

Energy and the Field of Force 174 



Energy of the Field of Force, 

Potential 173 

Energy and the Magnetic Cir- 
cuit 172 

Energy Ftelations 209 

Energy, Resistance and 70 

English Rule for • Charging. . . 151 

E. P. S. Battery 135 

Equalizer in Three-Wire Sys- 
tem, Storage Battery 50 

Equivalents, Atomic Weights 

and Chemical 89 

Equivalents, Electro-Chemical. 89 
Equivalent of Reactance of 

Capacity, Ohmic 337 

Equivalent of Reactance of In- 
ductance, Ohmic 336 

Ether and Current 167 

Ether, Luminiferous 40 

Ether Waves Produced by Elec- 
tricity 50 

Evolution, Gas 149 

Excitation of Field Coils in 

Compound Dvnamos 260 

Excitation of Shunt Coil, Ef- 
fect of Independent 260 

Excitation of Shunt Coil, Sep- 
arate 261 

External Resistance, Internal 
and 871 

Factor, Form 329 

Factor in Alternating-Current 

Arc, Power 544 

Factor. Power 330 

Factors of Magnetic Circuit, 

Three 175 

Fall of Potential, Drop and. . 79 

Faraday's Law 212 

Faure's Battery 130 

Faure-Sellon-Volckmar Battery, 

The 131 

Feeder Connections, Auxiliary 495 

Feeder Economy 496 

Feeders 483, 493 

Fiber Suspension 605 

Field Coils, Heating of 429 

Field Coils in Compound Dyna- 
mos, Excitation of 260 

Field Density 172, 176, 268 

Field Distortion 265 

Field of Force, The 167 

Field of Force, Building up the 173 
Field of Force and Lines of 

Force Due to Current 55 

Field of Force, Detection of 

the 174 

F'ieid of Force, Energy and 

the 174 

Field of Force, Iron and the. 175 
Field of Force, Motion of Con- 
ductor in 169 

Field of Force, Potential En- 
ergy of the 173 



748 



ELECTRICIANS' HANDY BOOK. 



Field of Force, Varying .... 207 
Field Magnets of Alternators. 436 
Field Magnet for Multipolar 

Dynamos 310 

Field Magnets, Laminated. . . 314 

F'ield Poles 222 

Field Poles, Action of on Arm- 
ature Core 265 

Field, The Rotary .. .363, 364, 366 

Field, Stray 184 

Field, Varying Densities of. . 267 

Field Winding, Break in 430 

Field Winding of Dynamos, 

252, 315 
Field Winding, Short Circuits 

in 430 

Field, Wrong Polarity of 417 

Fields of Force in Practice. . 209 
Fields, Windings for Multi- 
polar 237 

Figure of Merit 622 

Film Cut-Out 478 

Filament, Occlusion of Gases 
by Incandescent Lamp .... 525 

Filaments, Metallic 530 

Filaments, Oxide 530 

Filaments, Squirted 524 

Filaments, Tamidine 523 

Filing, Commutator 433 

Fishing for Bell Wires 719 

Five and Seven-Wire Systems. 502 
Flashing Incandescent Lamp 

Filaments 524 

Flashing, Lowering of Resist- 
ance of Incandescent- Lamp 

Filaments hy 525 

Flashing, Making Joints in 

Incandescent Lamps 525 

Fleming's Rule 212 

Floating Storage Battery.. 166, 410 

Forbes' Meter 514 

Force, Cutting Lines of.. 209, 224 
Force of the Electro-Magnet, 

Tractive 188 

Force, Electromotive. See B. 

M. F. 
Force. TTie Field of, etc. See 

Field of Force. 
F'orce, Leakage of Lines of. . 183 

Force, Magnetic 176 

Force, Memoria Technica for 

Lines of 171 

Force^ Relation Between Amp- 
ere Turns and Lines of . . . . 183 
Force, Spreading of Lines of. 188 
Force, Threading, Interlinking 

and Cutting Lines of 205 

Force, Utility of Conception of 

Lines of 171 

Form Factor 329 

Forming Storage Batteries. . 129 
Form of Alternating B. M. F. 

and Current 318, 319 

Formula, Bipolar Winding by. 247 



F'ormula, Multipolar Winding 

by 248 

Formulas, Bipolar Winding. . 247 
Formulas for Drum Armature 

Winding. General 246 

Forward EL M. F., Counter and 173 
Foucault or Eddy Currents, 

215, 271, 429 

Foucault's Photometer 572 

Frame, Short Circuits Between 

Armature Windings and . . 435 

Frequency 316 

Frequency, Length of Wave 

and 319 

Fuller's Mercury-Bichromate 

Battery 106 

Function of a Storage Battery 128 
Functions, Trigonometric .... 33 

Fundamental Note 677 

Furnaces, Electric 723 

Fuses, Safety 441, 448 

Fuses, Safety, in Cars 599 

Galvanic Pile 97 

Galvanometer 604 

Galvanometer, Astatic 605 

Galvanometer, Ballistic ..... 610 
Galvanometer, Constant of . . . 620 
Galvanometer, Deprez-D'Arson- 

val 611 

Galvanometer, Magneto Bell 

as 655 

Galvanometer, Reflecting. . 606, 609 
Galvanometer Resistance .... 622 

Galvanometer, Shunts 618 

Galvanometer, Shunt to the . . 636 

Galvanometer, Simple 604 

Galvanometer, Sine 616 

Galvanometer, Suspension Fiber 

for 605 

Galvanometer, Tangent 615 

Galvanometer, Thomson or 

Kelvin 609 

Galvanoscope 636 

Galvanoscope Cable and Line 

Tests 650 

Galvanoscope, Telephone as. . 653 

Gas Battery, Grove's 126 

Gas Evolution 149 

Gassing 149 

Gassing, Indications from . . 156 

Gauge, American Wire 85 

Gauges, Wire 85 

Gauss. The 178 

Generating Circle 322 

Generating Circle, Interpreta- 
tion of the 323 

Generation of Alternating Cur- 
rent 348 

Generator, Magneto 250 

Generator Without Motion.. 210 
Generator and Motor Con- 
nected 285 

Generator, Separately-Excited. 261 



INDEX. 



749 



Generators in Circuits, Appli- 
ances and 65 

Generators, Dynamo-Electric. . 218 

Gibbs' Battery 105 

Globe and . Carbon Holder... 547 

Globe, The Inclosing 559 

Gold-Plating 667 

Gould Storage Battery 132 

Graduation of Voltmeter 

Scales 463 

Gramme Ring, The 226 

Graphic Representation of 

Rate of Change 323 

Gravity Battery 114 

Gravity Cell, Modification of. 116 
Gravity Variation of Electro- 
lyte, Specific 146 

Greek Letters 34 

Grenet's Battery 108 

Ground Alarm 457 

Ground, Bad 598 

Ground, Hand Magneto Test 

for 657 

Ground Indicator, Alternating- 
Current 456 

Ground Indicator, Direct-Cur- 
rent 456 

Grounding Wires 721 

Grouping of Windings 350 

Grove's Batterv 102 

Grove's Gas Batterv 126 

Gutta-Percha Molds 673 

H Armature, Spindle or .... 222 

H and B Curves 178 

H and B Curves, Interpreta- 
tion of 179 

H and B Syonyms for 178 

Hand Magneto Test for 

Ground 657 

Hand Magneto Tests in Gen- 
eral 656 

Hare's Calorimeter 99 

Harmonic Signals for Party 

Lines 701 

Heat of Arc 536 

Heat in Transformers 384 

Heating, C?r 601 

Heating, Conditions Causing, 

584, 586 
Heating, Economy of Electric. 730 
Heating by the Electric Arc, 

Direct 727 

Heating, Electric Coolcing and 

Domestic 723 

Heating of Field Coils 429 

Heating of Motors 585 

Heating of Windings of Stator. 

Local 436 

Helios-Upton Battery 133 

Henry. Inductance and the.. 332 

Hertz Receiver 732 

High Potential, Advjintages of. 476 
High-Resistance Measurements 643 



High-Voltage Determinations 

with Potentiometer 638 

High-Voltage Parallel Systems 503 

Hissing Arc 543 

Holder, Globe and Carbon... 547" 

Holders, Brush 305 

Holders, Brushes and Brush. 420 

Hook-Switch, The 696 

Horse-Power of Car Motors. . 586 

Horse-Power Lines 274 

Hot Resistance 596 

Hot-Wire Voltmeter, The Stan- 
ley 466 

Hot-Wire Voltmeters 466 

House Connections, Telephone 693 

Hushes Microphone 680 

Human Voice, The 678 

Running Transmitter 682 

Hydrogen Liberated by tlie 

Coulomb 88 

H^ydrogeh to Oxygen, Propor- 
tion of 88 

Hydrometers for Storage Bat- 
teries 147 

Hysteretic Constant 186 

Hysteresis 185 

Hysteresis Curves 185 

Hysteresis. Loss of Energy 

Due to 186 

Hysteresis and Other Receiv- 
ers 736 

Idle Wire 229 

Illuminating Power, Standards 

of 563 

Impedance 339 

Impressed E. M. F., Varia- 
tions in 216 

Impurities in Electrolyte and 

Tests 155 

Incandescence, Open-Air .... 562 

Incandescent Lamp, The 523 

Incandescent Lamp Circuits, 

Arc and 472 

Incandescent Lamps, Candle- 
Powers of 576 

Incandescent Lamps, Distribu- 
tion of Light from 583 

Incandescent Lamps, Watts per 

Candle-Power in 580 

iDcandescent Lighting 523 

Incandescent Lighting, "Muni- 
cipal" Series 479 

Incandescent Lighting, Series. 477 

Inclosed-Arc, Action of 546 

Inclosed-Arc Carbons . . . .547, 559 

Inclosed-Arc Lamp 545 

Inclosed-Arc Lamp, Carbons 

for 560 

Inclosing Globe, The 559 

Incubator, The Electric 729 

Independent Circuits 492 

Independent Excitation of 
Shunt Coil, Effect of 260 



750 



ELECTRICIAN Si' HANDY BOOK. 



Indications From Gassing. . . . 156 
Indicator, Alternating-Current 

Ground 456 

Indicator, Direct-Current 

Ground 456 

Individual Transformers .... 505 
Individual Voltages of Lamps. 490 
Inducing Electric Energy, Con- 
ditions for 206 

Inductance 3.32 

Inductance and Capacity, Com- 
position of Resistance 343 

Inductance Compensator, The. 471 
Inductance and the Henry... 332 
Inductance, Ohmic Equivalent 

of Reactance of 336 

Inductance, Reactance of .... 335 
Inductance, Reactance in Sub- 
divided Conductor 336 

Inductance, Turns of a Cir- 
cuit and 334 

Induction 205 

Induction, Ampere's Rule 

Adapted to 213 

Induction Coils in Bracket 

Telephones 688 

Induction Coil, Dimensions of 

Telephone 686 

Induction Coil, Effect of Tele- 
phone 688 

Induction Coil, The Telephone 684 
Induction, Electro-Magnetic... 205 
Induction, Examples of ..... 211 

Induction Interference 714 

Induction, Laws of 212 

Induction Motor, The. 363, 366, 369 
Induction Motor, Lenz's Law 

and the 369 

Induction Motor, Polyphase . . 4.36 

Induction Motor Rotors 436 

Induction Motor, Three-Phase. 365 
Induction, Two Systems of . . . . 210 
Inductive Capacity, Specific. 48 

Inductivity 48 

Inductor Alternator 356 

Iron and the Field of Force.. 175 

Iron Negative Plates 101 

Iron, Saturation of 177 

Inspection of Transformers. . 438 
Insulation Resistance of Cable 646 
Insulation of Storage Battery 

Cells r ". 161 

Insulation Tests. Line 643 

Insulation for Transformers. . 390 

Insulation of Windings 441 

Insulator of Magnetism, ISo.. 177 

Insulators .....'' 511, 603 

Intensity 53 

Internal and External Resist- 
ance 71 

Interchangeability of Dynamo 

and Motor ..." .' 218 

Interchangeability of Parts. . 439 
Interference, Conduction .... 714 



Interference, Induction 714 

Interlinking and Cutting Lines 

of Force. Threading 205 

Interpretation of B and H 

Curves 179 

Invention of Microphone .... 679 
Inverted Addition and Sub- 
traction 23 

Jablochkoff Candle, The 561 

Jacket Type Transformers, 

Shell or 378 

Joints in Line Wire 508 

Kelvin Absolute Electrometer, 
Thomson or 617 

Kelvin Galvanometer, Thom- 
son or 609 

Kirchofe's Laws 83 

Lag 325 

Lag, Angle of Lead and .... 326 
Lag and Lead, Basis of .... 327 
Lag and Lead, Causes of .... 341 
Lalande and Chaperon Bat- 
tery, Modifications of .... 119 
Laminated Field Magnets . . . 314 

Lamp Annunciator 709 

Lamp, Carboning a 561 

Lamp Circuits, Arc and Incan- 
descent 472 

Lamp on Constant Potential- 
Circuit, Arc 553 

Lamp, Direct Photometering of 

Arc 572 

Lamp, Efficiency of Nernst. . . 533 
Lamp, The Incandescent .... 523 
Lamp, Inclosed-Arc, Carbons 

for 560 

Lamp. Making Joints by 

Flashing in. Incandescent. . . 525 
Lamps, Metallic Filaments in 

Incandescent 530 

Lamp, The Nernst 530-533 

Lamp, Pasted Joints in, Incan- 
descent 526 

Lamp, Photometry of Arc . . . 576 
Lamp, Putting. Into Service.. 560 

Lamp Signal System 713 

Lamp, The Sun 562 

Lamp, The Wallace 562 

Lamps, Adjusting 559 

Lamps. Candle-Powers of In- 
candescent 576 

Lamps, Carbon-Feed 549 

Lamps, Commercial Rating of. 

Arc 542 

Lamps, Constant-Current or 

Series Arc 551 

Lamps. Constant-Potential Arc 555 
Lamps, Direct-Current, Nernst 532 
Lamps, Distribution of Light 
from Alternating-Current 
Arc 544 ! 



INDEX. 



751 



Lamps, Distribution of Light 

from Incandescent 583 

Lamps, Efficiency of Alternat- 
ing-Current Arc 545 

Lamps, Electroplated and 

Other Joints in Incandescent 526 
Lamps, Features of Series or 
Constant-Current System for 

Arc 475 

Lamps. Inclosed-Arc 543 

Lamps, Individual Voltages of 490 
Lamps, Maliing Incandescent . . 526 
Lamps Without Mechanism . . 561 

Lamps, Noise in Arc 545 

Lamps, Relief 478 

Lamps, Vacuum Nernst 533 

Lamps. Watts per Candle- 

Power in Incandescent 580 

Lap Winding 239, 249 

Lap Winding, Multipolar . . . 246 

Lap Winding, Wave and 238 

Law, Faraday's 212 

Law and the Induction Motor, 

Lenz's 369 

Law, KirchofE's 83 

Law, Lenz's 213 

Law, Ohm's 74 

Law, Right-handed Screw . . 204 

Laws of Induction 212 

Lead 325 

Lead, Basis of Lag and 327 

Lead, Causes of Lag and .... 341 

Lead and Lag, Angle of 326 

Leading-in Wires 526 

Leakage of Lines of Force .... 183 
Leakage. Measurement of Re- 
sistance 645 

Leecon Disk. The 565 

Length. Voltage Drop and Arc 538 

Length of Wave 318 

Lenz's Law 213 

Lenz's Law and the Induction 

Motor 369 

Letters, Greek 34 

Light of Alternating-Current 

Arc Lamps. Distribution of. 544 
Light from Arc Lights, Dis- 
tribution of 582 

Light in Direct-Current Open 

Arc, Distribution of 541 

Light, Distribution of 534 

Lights, Distribution of Light 

from Arc 582 

Light, Efficiency of Arc 537 

Light Given by Arc Proper . . 543 
Light, Mechanical Equivalent 

of 577 

Light, Quality of Arc 580 

Light, Watts per Candle- 

Power in Arc 579 

Lighting Circuits. Connections 

for Charging from 157 

Lighting Current, Standard 
Series 477 



Lighting, Incandescent 523 

Lighting. "Municipal" Series 

Incandescent 479 

Lighting, Series Incandescent. 477 
Lightning Arrester, Double- 
Pole 522 

Lightning Arrester, Low- 
Equivalent Alternating-Cur- 
rent 521 

Lightrfing Arrester, Tank . . . 522 
Lightning Arrester, Westing- 
house 521 

Lightning Arresters .....jIS, 591 
Limitations of Series Distri- 
bution 474 

Line Connections 362 

Line Insulation Tests 643 

Line of Ohms 278 

Line Resistance Tests 643 

Line Tests, Galvanoscope Cable 

and 650 

Line Wire. Joints in 508 

Lines of Force in Armature, 

End Leakage of 272 

Lines of Force. Cutting. .209, 224 
Lines of Force Due to Current, 

Field of Force and 55 

Lines of Force, Leakage of. . 183 
Lines of Force about a Mag- 
net, Illustrating 188 

Lines of Force, Memoria 

Technica for 171 

Lines of Force Produced bv a 

Curved Conductor 169 

Lines of Force. Relation Be- 
tween Ampere Turns and. . 183 
Lines of Force, Spreading of. 188 
Lines of Force, Threading, 

Interlinking and Cutting. . 205 
Lines of Force, Utility of 

Conception of 171 

Lines. Harmonic Signals for 

Party 701 

Lines, Horse-Power 274 

Lines, Party 700 

Lines. Polarized Bells for 

Party 700 

Load, Slow Speed Without.. 418 
Local Action of Primary Bat- 
tery 96 

Logarithms 81 

Longer Arcs, Resistance of . . . 543 
Long-Shunt Compound Wind- 
ing 256 

Long-Shunt Windings, Action 

of Short-Shunt and 257 

Loop System 483 

Loop Test, Varley 656 

Loose Carbon Transmitters. . . 681 
Loss of Energy Due to Hyster- 
esis 186 

Loss of Magnetic Polarity... 417 
Low-Equivalent Alternating- 
Current Lightning Arrester 521 



752 



ELECTRICIANS' HANDY BOOK. 



Luminescence 530 

Luminiferous Ether 40 

Lnminomfeter, The 572 

Lummer-Brodhim Screen, The. 565 

Machine, Starting a 427 

Machine, Stopping a 416 

Machines, Conventional Repre- 
sentations of ,. 264 

Machines in Series, Shunt'- 

Woimd 403 

Magnet, Action of a Current on 

the 202 

Magnet, Annular Chambered. . 191 

Magnet, Blow-Out 596 

Magnet, Effect of 538 

Magnet, The Electro- 188 

Mag-net. Illustrating Lines of 

Force About a 188 

Magnet. Magnetizing by Coil 

and Electro- 197 

Magnet for Multipolar Dyna- 
mos, Field 310 

Magnet, The Natural 194 

Magnet, The Permanent .... 194 
Magnet Poles on Each Other, 

Action of 195 

Magnet, Spiral Electro- .... 189 
Magnet, Tractive Force of the 

Electro- 188 

Magnetic Blow-Out Arrester. 518 

Magnetic Circuit, The 172 

Magnetic Circuit, Energy and 

the 172 

Magnetic Circuit, Nature of 

the 174 

Magnetic Circuit, Permeance 

of a 184 

Magnetic Circuit, Three Fact- 
ors of 175 

Magnetic Force 176 

Magnetic Induction, Electro-. 205 
Magnetic Needle in Rotating 

Field, The 364 

Magnetic Polarity, Loss of. . 417 
Magnetic Poles, Attraction 

and Repulsion of 202 

Magnetic Release Starting Box 398 
Magnetic Release Underload 

Circuit Breaker 452 

Magnetic Tractive Power, 

Electro- 192 

Magnetism, Ampere's Theory 

of 200 

Magnetism, Ampere's Theory 

of Terrestrial 201 

Magnetism, Constancy of . . . . 199 
Magnetism, No Insulator of. . 177 

Magnetism, Residual 185 

Magnetized 199 

Magnetizing by Coil and Elec- 
tro-Magnet 197 

Magneto Bell as Galvanometer, 
The 655 



Magneto Generator, The .... 250 
Magneto Test for Ground, 

Hand 657 

Magneto, The Telephone 689 

Magneto Test for Cross Con- 
nections, . Hand 658 

Magnetos, Regulation of Sep- 
erately-Excited Dynamos 

and 262 

Magneto Tests, Hand 656 

Magnets of Alternators, Field 436 

Magnets, Concentric, in Lamps 550 
Magnets by Double Touch, 

Making 196 

Magnets, Examples of Perman- 
ent 198 

Magnets, Laminated Field... 314 

Magnets, Making U-Shaped. . 196 

Magnets,. Memoria Technica of 201 

Magnets, Multipolar 192 

Magnets, Preservation of 198 

Magnets by Single Touch, 

Making 195 

Magnets, Steel for 197 

Magnets,' U-Shaped Electro-. 189 
Main Circuit, Exciting Series 

Coils from 261 

Main, and Leads, Feeders .... 483 

Marconi's Coherers 736 

Material of Commutator .... 419 

Material of Vessels for Plating 671 

Measurement, Angular 32 

Measurement, Ballistic 613 

Measurements, High Resist- 
ance 643 

Measurement with Potentiom- 
eter, Current 640 

Measurement of Resistance 

Leakage 645 

Measurement of Resistance, 

Voltmeter 642 

Mechanical Equivalent of 

Light 577 

Mechanical Release Underload 

Circuit Bre0,ker 453 

Meidinger's Battery 114 

Mercury-Bichromate Battery, 

Puller's 106 

Merit, Figure of 622 

Memoria Technica of Mag- 
nets 201 

Memoria Technica for Lines 

of Force 171 

Mesh Connection, Delta or. . . . 361 

Metal Brushes, Trimming.,.. 307 

Metals Deposited in Plating. 662 

Meter Bridge, The 634 

Meter, Edison's 513 

Meter, Forbes' 514 

Meter, Shallenberger's 517 

Meter, Thomson's 515 

Meters, Electric 513 

Method, Null 634 

Microfarad 49 



INDEX. 



753 



Microphone, Hughes 680 

Microphone, Invention of .... 679 
Mil System, Application of 

Circular 84 

Mil System, Circular 83 

Mil, Examples of Area of Cir- 
cular '. 84 

Mil, Area of Circular 84 

Moisture in Transformers .... 438 

Molds in Bath, Placing 674 

Molds, Elastic 673 

Molds, Gutta-Percha 673 

Molds, Metal 671 

Molds, Plaster 672 

Molds, Plating on 674 

Molds, Preparing 673 

Motor and Booster 501 

Motor Connected, Generator 

and 285 

Motor, Construction of Car . . 588 
Motor Dynamos as Boosters.. 408 

Motor, The Electric-Car 584 

Motor Heating, Cause of . . . . 584 

Motor, The Induction 363 

Motor, Interchangeability of 

Dynamo and 218 

Motor, Lenz's Law and the 

Induction 369 

Motor Without Load, Speed 

Regulation of 418 

Motor, Operation of Synch- 
ronous 370 

Motor, Refusal of, to Start . . 417 
Motor, Reversibility of Dyna- 
mo and 285 

Motor Rotors. Induction 436 

Motor, Self-Starting Single- 
Phase 435 

Motor, Self-Starting Synch- 
ronous 373 

Motor, Single-Phase Synchron- 
ous 371 

Motor, Synchronous Polyphase. 372 
Motor, Temperature of Dyna- 
mo or 439 

Motor, Three-Phase Induction 365 
Motor and Torque, Direct- 
Current 285 

Motor Transformer 400, 401 

Motor Troubles 600 

Motors, Accidents to 415 

Motors, Construction of In- 
duction 369 

Motors, Determining the Heat- 
ing of 585 

Motors, Horse-Power of Car.. 586 

Motors, Idle 418 

Motors, Induction 366 

Motors, Polyphase Induction. . 436 
Motors, Starting and Stop- 
ping 397, 418 

Motors. Synchronous ....369,436 

Motorman's Duties 597 

Mounting of Ring Armature. 230 



Moving Electrodes 103 

"Municipal" Series Incandes- 
cent Lighting 479 

Multiple Series 67 

Multiple Series System 478 

Multiple Switchboard, The . . 706 
Multipolar Construction. .252, 350 
Multipolar Construction, Ad- 
vantages of 252 

Multipolar Dynamo Connec- 
tions 264 

Multipolar Dynamo, Modern. 250 
Multipolar Dynamos, Field 

Magnet for 310 

Multipolar Fields, "Windings 

for 237, 315 

Multipolar Lap Windings 246 

Multipolar Magnets 192 

Multipolar Ring Armature. . . 231 
Multipolar Winding bv Formu- 
la \ 248 

Multipolar Windings 245 

Mutual Action of Currents . . . 199 

Nature of the Magnetic Cir- 
cuit 174 

Natural Magnet, The 194 

Negative Carbon, Positive and, 

535, 560 
Negative and Positive Plates. 9o 
Negative Plate, Aluminium . . 101 

Negative Plate, Carbon 103 

Negative Plates, Iron 101 

Nernst Lamp 530, 533 

Nernst Lamp, Direct Current. 532 

Nernst Lamp Ballast 532 

Nernst Lamp Glower 530 

Nernst Lamp Glower Terminals 531 

Nernst Lamp Heaters 531 

Nernst Lamp Vacuum 533 

Neutral Points 268 

Neutral Wire in Three-Wire 

System 497-499 

Neutral WMre in Y System ... 362 

Nickel-plating 664 

Nitric Acid Depolarizers, 

Sulphuric and 110 

Noise in Arc Lamps 545 

Nomenclatu^re for Drum Arma- 
ture Winding 246 

Nomenclature of Primary Bat- 
tery 95 

Non - Conductors, Conductors 

and 50 

Notation, Exponential 29 

Note, Fundamental 677 

Null Method 634 

Numerical Value of Circular 
Functions 34 

Occlusion of Gases by Fila- 
ment 525 

Ohm, The .71 



•754 



ELECTRICIANS' HANDY BOOK. 



Ohm, British Association 

Standard 627 

Ohm's Law 74 

Ohm's Law, Examples of . . . . 75 
Ohm's Law, Five Forms of.. 76 
Ohmic Equivalent of React- 
ance of Capacity 337 

Ohmic Compensator, The 471 

Ohmic Equivalent of React- 
ance of Inductance 336 

Ohms, Line of 278 

Ohm-Volt Curves 2S4 

Oil 560 

Oil Cooling 384 

Oil for Filling Transformers, 

389, 437 

Oiling 440, 674 

Oil Switches 447 

Open Arc, The Direct-Current 540 
Open Are, Distribution of 

Light in Direct-Current... 541 

Open-Air Incandescence 562 

Open Circuit, Discharge of 

Storage Battery on 144 

Open and Closed Circuits 64 

Open-Coil Armatures 222 

Open-Wound Four-Part Arma- 
ture 230 

Opening Shunt Coil, Discon- 
necting or 260 

Operation, Two-Phase 436 

Opposition, Quadrature and . . 327 

Outer Circuit 68 

Outer Circuit, Short Circuits in 432 

Overtones 677 

Over-Compounding 259 

Overload Circuit Breakers.... 451 
Overload and Underload Cir- 
cuit Breakers 448 

Oxide Filaments 530 

Oxygen, Proportion of Hydro- 
gen to 88 

Pacinotti Armature, The 225 

Pancake Coils 381 

Panels, Switchboard 445 

Parallel Circuits, Calculation 

of Resistance of 81 

Parallel-Circuit System 554 

Parallel Coupling of Com- 
pound Dynamos 402 

Parallel Coupling of Dynamos 402 
Parallel Coupling of Shunt 

Dynamos 402 

Parallel Distribution 481 

Parallel Distribution, Disad- 
vantages of 482 

Parallel Distribution, Ele- 
mentary Case of 482 

Parallel, Series and 68 

Parallel and Shunt 67 

Parallel System, Potential 

Drop in 482 

Parallel Systems, Anti- 488 



Parallel Systems, High-Voltage 503 
Parts, Interchangeability of. . 439 

Parts of Primary Battery 93 

Party Lines 700 

Party Lines, Harmonic Sig- 
nals for 701 

Party Lines, Polarized Bells 

for 700 

Partz's Battery 109 

Pasted Plates 135,139 

Percentage 20 

Permeability 175, 177 

Permeability Curves 180 

Permeance 175 

Permeance of a Magnetic Cir- 
cuit 184 

Permeance of Ring Core 228 

Phase 325 

Photometer Apparatus 567 

Photometer, Bar 563 

Photometer Bar, Calculating- 
Scale of 568 

Photometer, Bouguer's 570 

Photometer, Diffractive 574 

Photometer, Foucault's 572 

Photometer Observations .... 569 

Photometer, Principle of 563 

Photometer, Pupillary 573 

Photometer, Shadow 570 

Photometering of Arc Lamp, 

Direct 572 

Photomteric Screens 564 

Photometric Standards 570 

Photometric Standards, Table 

of 570 

Photometry of Arc Lamp .... 576 

Pile, Galvanic 97 

Pile, Volta's 97 

Pile, Zamboni's . 99 

Pilot Wires, Pressure Lines or 470 

Pitch 677 

Plante's Battery 12S 

Plate, Cadmium 156 

Plate, Sounding 677 

Plates, Buckling of 153 

Plates, Negative and Positive. 95 

Plates, Pasted 135, 139 

Plates, Suspended 138 

Plating Apparatus 661 

Plating on Molds 674 

Platinum-Plating 668 

Poggendorff's Battery, Depolar- 
izing Mixtures in 109 

Poggendorff's Battery, Exciting 

Solutions in 109 

Poggendorff's Battery, Modi- 
fications of 106 

Points, Controller 593 

Points, Driving 593 

Points, Neutral 268 

Polarity of the Circuit, The.. 159 
Polarity Due to Windings, 

Armatui-e 265 

Polarity of Field, Wrong. . . . 417 



INDEX. 



755 



Polarity, Loss of Magnetic... 417 

Polarity, Tests for 404 

Polarization of Primary Bat- 
tery 96 

Polarized 199 

Polarized Bell 691 

Polarized Bells for Party Lines 700 

Pole Armatures 301 

Pole Pieces, Eddy Currents in 272 
Pole Single-Phase Armature.. 354 
Poles, Attraction and Repul- 
sion of Magnetic 202 

Poles, Development of Field.. 240 
Poles on Each Other, Action 

of Magnet 195 

Poles, Field 222 

Polyphase Induction Motors . . 436 
Polyphase Synchronous Mot- 
ors 372 

Position of Anode and Cathode 670 
Positive and Negative Carbons, 

535, 560 
Positive and Negative Plates... 95 
Potassium Bichromate Solu- 
tions 110 

Potential, Advantages of High 476 

Potential, Analogies of Drop of 60 
Potential Circuit, Arc Lamp 

on Constant 553 

Potential Circuit, Constant . . 78 

Potential, Drop of 60 

Potential, Drop and Fall of . . 79 
Potential Drop in Parallel 

System 482 

Potential, E. M. F. and Differ- 
ence of 61 

Potential Energy of the Field 

of Force 173 

Potential Methods, Uniform . . 492 
Potential Regulator, Alternat- 
ing-Current 454 

Potentiometer, The 637 

Potentiometer, Current Meas- 
urement with the 640 

Potentiometer, High - Voltage 

Determinations with 638 

Potentiometer, Principle of. . . 637 

Power 77 

Power Calculations, Examples 

of 79 

Power Consumed in Arc 538 

Power Curves 345 

Power, Electro-Magnetic Tract- 
ive 192 

Power, Examples of 77 

Power F'actor 330 

Power Factor in Alternating- 
Current Arc . o 544 

Power Required for Cooking. 723 
Power, Standards of Illumin- 
ating 563 

Powers of Ten or Exponential 

Notation 29 

Practical Processes 676 



Preparations for Silver-Plat- 

ing 666 

Preparing Storage Battery 

Electrolyte 155 

Preservation of Magnets 198 

Pressure, Brush 420 

Pressure Lines or Pilot Wires. 470 
Prevention of Sulphating. . . . 151 

Primary Battery, The 125 

Primary Battery, Amalgama- 
tion in 96 

Primary Battery Cell, The.. 93 
Primary Battery, Exhaustion 

of 96 

Primary Battery, Local Action 

of 96 

Primary Battery, Nomenclat- 
ure of 95 

Primary Battery, Parts of . . 93 
Primary Battery, Polarization 

of 96 

Production of Alternating E. 

M. F. and Current 318 

Production of Current 52 

Production of Electromotive 

Force 56 

Prony Brake, The 38 

Proportional Coils 636 

Proportion of Hydrogen to 

Oxygen 88 

Protectors. Lightning 518 

Pump, The Mercury Air 528 

Pupillary Photometer 573 

Quadrature and Opposition... 327 

Quality of Arc Light 580 

Quality of Carbons 538 

Qualities of a Circuit 331 

Quantity of Electricity, Mean- 
ing of 44 

Quantity of Electricity, The 

Storage of 47 

Quantity, Electric 41 

Quantity. Unit of 45 

Quantities, Multiplication of 

Alternating 244 

Quantities, Summation of Al- 
ternating 342 

Racing 720 

Radian System of Angular 

Measurement 32 

Radiator, Electric 730 

Radiguet Battery 108 

Radius Vector and Resultant. 324 

Rail-Joint Test 644 

Rate of Change. . .. , 323 

Rate of Change, Graphic Rep- 
resentation of 323 

Rate Units, Current and .... 50 
Rating of Arc Lamps, Com- 
mercial 542 

Ratio of Transformation .... 379 

Reactance 332 



756 



ELECTRICIANS' HANDY BOOK. 



Reactance of Capacity 337,338 

Reactance Coil or Economy 

Coil 545 

Reactance of Inductance . . 335, 336 
Reactance in Subdivided Con- 
ductor, Inductance 336 

Reaction Diagrams, Armature 266 

Receiver, Tlie Teleplione 683 

Receiver, a Dynamo, Telephone 212 

Receiver, Hertz 732 

Receiver, Principle of Tele- 
phone 678 

Receivers, Hysteresis and 
Other Wireless Telegraphy . . 736 

Receiving Apparaus 733 

Rectifier, The 394 

Reflecting Galvanometer . . 606-609 

Regeneration 126 

Regulation of Voltage, Auto- 
matic 492 

Regulation of Current in Elec- 
troplating 661 

Regulator, Alternating - Cur- 
rent Potential 454 

Regulators or Boosters 406 

Relation Between Ampere 
Turns and Lines of Force . . 183 

Relations, Energy 209 

Relief Lamps ■ 478 

Reluctance and Reluctivity... 178 

Repeating Coils 705 

Reproduction 660 

Repulsion of Magnetic Poles, 

Attraction and 202 

Residual Magnetism , 185 

Resistance 69 

Resistance of Arc Proper .... 537 

Resistance Boxes 626,630 

Resistance of Cable, Insulation 64 
Resistance, Circuit Without. . 71 
Resistance Coil in Arc Lamp. 553 

Resistance Coils 626-631 

Resistance Coils, Modern Ar- 
rangement 628 

Resistance Coils, Practical 

Notes on 631 

Resistance, Compensating . . . 619 

Resistance and Energy 70 

Resistance by Flashing, Low- 
ering of 525 

Resistance, Galvanometer . . . 622 

Resistance, Hot 596 

Resistance, Inductance and Ca- 
pacity, Composition of 343 

Resistance, Internal and Ex- 
ternal 71 

Resistance Leakage, Measure- 
ment of 645 

Resistance of Longer Arcs... 543 
Resistance of Parallel Circuits, 

Calculation of 81 

Resistance of Short Arcs .... 543 

Resistance, Spurious 270 

Resistance, Starting ; . 367 



Resistance of Storage Batteries 132 

Resistance Tests, Line 643 

Resistance, Voltmeter and Am- 
meter Determination of ... 642 
Resistance, Voltmeter Measure- 
ment of 642 

Resistance Wire 627 

Resonance, Electric 339 

Resultant, Radius Vector and 324 
Reverse Current Circuit 

Breaker 454 

Reverser, Car 596 

Reversing the Car 598 

Reversing Direction of Current 416 
Revolving Field, Rotary and . 366 

Rheostat 624 

Rheostat Controller 596 

R. I. Drop Calculations, Ex- 
amples of 82 

R. I. Drop and Counter E. M. 

F 79 

Ring Armature, Commutator 

Connections of 227 

Ring Armature, Current in. . 229 
Ring Armature, Mounting of. 230 
Ring Armature, Multipolar... 231 
Ring Armature, Open-Wound 

Four-Part 230 

Ring Armatures, Cores of . . . 228 

Ring Core. Permeance of 228 

Ring Oiling 440 

Ring, The Gramme 226 

Rings, Collecting or Slip 219 

Rings, Collector 419 

Rotary Converter 390 

Rotary Converter, Functions 

of a 394 

Rotary Converter, Starting a. 394 
Rotary Converter in Three- 
Wire System 393 

Rotary and Revolving Field.. 366 
Rotary Field, Armature in ... . 364 

Rotary Field, The 363 

Rotary Transformer, The 391 

Rotary Transformers, Rela- 
tions of Voltage and Cur- 
rent in 392 

Rotary Transformer, Use of . . 391 
Rotating Field, The Magnetic 

Needle in 364 

Rotation, Reversal of Arma- 
ture 404 

Rotor and Stator 355 

Rotors of Alternators, Trouble 

in 435 

Rotors, Induction Motor 436 

Rule, Ampere's 203 

Rule for Charging Storage Bat- 
teries, English 151 

Rule, Clerk Maxwell's 213 

Rule, Fleming's 212 

Safety Fuses 441, 448 



INDEX. 



757 



Sand Type of Daniell's Bat- 
tery 114 

Sandpapering Commutator.... 432 

Saturation of Iron 175, 177 

Saw-Tooth Arrester, Comb or. 518 
Scale of Pliotometer Bar, Cal- 
culating 568 

Scale, Translucent, Galvanome- 
ter 463 

Scales, Graduation of Volt- 
meter 463 

Screen, The Lummer-Brodhun. 565 

Screens. Photometric 564 

Sediment in Storage Batteries 153 
Sensibility, Regulation of, in 

Galvanometer 610 

Sensitiveness, Conditions of in 

Galvanometer 636 

Self-Excited Dynamos, Sepa- 
rately- and 263 

Self-Regulation of Compound- 
wound Dynamos 257 

Self-Starting Single-Phase Mo- 
tor 435 

Separately-Excited Generators 

261-263 

Series 67 

Series Arc Lamps, Constant- 
Current or 551 

Series or Constant-Current Sys- 
tem for Arc Lamps, Features 

of 475 

Series Distribution 473 

Series Distribution, Calcula- 
tions for 475 

Series Distribution, Limitations 

of 474 

Series Distribution, Objections 

to 481 

Series Incandescent Lighting . . 477 
Series Incandescent Lighting 

"Municipal" 479 

Series Lighting Current, Stan- 
dard 477 

Series-Multiple 67 

Series-Multiple System 479 

Series and Parallel 68 

Series-Parallel Controller .... 594 
Series, Shunt-Wound Machines 

in 403 

Series Telephone Circuit 695 

Series Winding, Action of ... . 254 
Series Winding of Dynamos. . . 252 
Service, Putting Lamp into . . . 560 
Service, Taking Storage Battery 

out of 160 

Seven-Wire Systems, Five and 502 

Shadow Photometer 570 

Shaft, End Motion in Arma- 
ture 423 

Shallenberger's Meter 517 

Shock, Treatment of Electric. 442 
Shell or Jacket Type Trans- 
formers 378, 379 



Short Arcs, Resistance of . . . . 543 
Short-Circuiting of Single Cells 152 

Short Circuits 69, 433 

Short Circuits in Armature... 423 
Sbort Circuits between Arma- 
ture Windings and Frame.. 435 
Short Circuits in Field Wind- 
ing 430 

Sbort Circuits in Outer Circuit 432 
Short Circuits in Transformers 438 
Short-Shunt Compound Wind- 
ing 256 

Short-Shunt and Long-Shunt 

Windings, Action of 257 

Shunt Coil, Disconnecting or 

Opening 260 

Shunt Coil, Effect of Indepen- 
dent Excitation of 260 

Shunt Coil, Separate Excita- 
tion of 261 

Shunt to the Galvanometer . . , 636 

Shunt, Galvanometer 618 

Shunt Dynamo, Total Charac- 
teristic Curve of 283 

Shunt Dynamo, Total Current 

Characteristic Curve in. . . . 282 
Shunt Dynamos, Parallel Cou- 
pling of 402 

Shunt Winding, Action of . . . . 255 
Shunt Winding of Dynamos. . 254 

Shunted Ammeter 469 

Shunt- Wound Dynamo, Critical 

Point of 281 

Shunt-Wound Dynamo Charac- 

teric Curves 280 

Shunt-Wound Machines in Se- 
ries 403 

Siemens's Dynamometer .... 622 
Siemens's Plan for Resistance 

Boxes 627 

Signal System, Lamp 713 

Signals, Emergency and Dan- 
ger 441 

Signals for Party Lines, Har- 
monic 701 

Signals, Wave Transmission of 731 

Silver-Plating 665 

Silver-Plating, Preparation for 666 

Silver Voltameter 90 

Simple Batteries 93 

.Sine-Curve, The 321 

Sine-Curve, Vector Diagram of 325 
Sine Galvanometer, or Com- 
pass, The 616 

Single Cells, Short-Circuiting 

of 152 

Single - Dynamo Three - Wire 

System 499 

Single-Phase Armature 348 

Single-Phase Armature, Pole.. 354 
Single-Phase Motor, Self-Start- 
ing 435 

Single-Phase Synchronous Mo- 
tor 371 



758 



ELECTRICIANS' HANDY BOOK. 



Single Surface Condenser 45 

Single Touch, Making Magnets 

by 195 

Siphon Battery, Baudet 107 

Six-Wire Connection of Three- 

Phase Alternator Winding. . 359 
Size of Conductors for Plating 669 

Slip Rings, Collecting or 219 

Slow Speed without Load. . . . 418 

Smee's Battery 103 

Smoothing Commutator 433 

Soldering 441, 721 

Soldering Iron, The Electric . . 728 
Solenoid Ammeters, Total-Cur- 
rent 467 

Solid Back Transmitter, The. 683 
Solutions in Poggendorff Bat- 
tery, Exciting 109 

Solutions, Potassium Bichro- 
mate 110 

Sound 677 

Sounding Plate 677 

Sparking, Air Gap and 310 

Sparking of Commutator 424 

Specific Inductive Capacity .... 48 
Speed Control, Crocker-Wheel- 
er 414 

Speed of a Current 54 

Speed without Load, Slow.... 418 
Speed Regulation of Motor 

without Load 418 

Spherical Candle Power 574 

Spindle or H Armature 222 

Spiral Electro-Magnet 189 

Spreading of Lines of Force. . 188 

Spring Jacks 710 

Squirted Filaments 524 

Standard English Candle, The. 567 
Standard Series Lighting Cur- 
rent 477 

Standard Voltage and Allow- 
able Temperature 584 

Standards of Illuminating 

Power 563, 570 

Stanley Hot-Wire Voltmeter, 

The 466 

State, Stationary 543 

Static Charge, E.M.F. and the 58 
Static Electricity, Dynamic 

and 56 

Stations, Connection of 734 

Stator. Local Heating of Wind- 
ings of 436 

Stator, Rotor and 355 

Star Connection, Y or 359 

Starting Box 397, 398 

Starting Compensator 368 

Starting a Dynamo 427, 428 

Starting Motors 397 

Starting Resistances 367 

Starting and Stopoing Motors 418 

Starting Torque 367 

Start, Refusal of Motor to.417, 598 
Steel in Dynamos, Soft 181 



Steel for Magnets 197 

Steeling 669 

Step-Down Transformers, Step- 
Up and 378 

Step-Down and Step-Up Trans- 
formation 400 

Step, Alternators in 405 

Stone's Common Battery Sys- 
tem 698 

Stop Adjustment, Clutch 560 

Stop, Emergency 600 

Stopping Motors, Starting and, 

416, 418 
Storage Battery, Action of a . . 125 
Storage Battery, American... 134 

Storage Battery Cells 161 

Storage Battery, The Charge of 145 
Storage Battery, Charging. . . . 166 
Storage Battery Connections, 

Booster and 410 

Storage Battery Connections, 

Making 161 

Storage Battery, Determination 

of Discharge of 145 

Storage Battery, Disintegration 

of 153 

Storage Battery, Edison's 140 

Storage Battery, End Cells of. 164 
Storage Battery Equalizer in 

Three-Wire Systems 501 

Storage Battery, F'loating 166 

Storage Battery, Function of a 128 

Storage Battery, Gould 132 

Storage Battery on Open Cir- 
cuit, Discharge of 144 

Storage Battery, Overcharge of 151 
Storage Battery, Requirements 

of a 128 

Storage Battery, Setting Up a. 153 
Storage Battery, Specific Grav- 
ity Variation of Electrolyte 

in 146 

Storage Battery, Suspended 

Plates in 138 

Storage Battery, Taking out of 

Service 160 

Storage Batteries, Chemical Ac- 
tion of 131 

Storage Batteries, Copper 139 

Storage Batteries, The Dis- 
charge of 144 

Storage Batteries, Forming... 129 
Storage Batteries, Manufac- 
turer's Data with 144 

Storage Batteries, Notes on. . 163 
Storage Batteries, Resistance 

of 132 

Storage Batteries. Sediment in 153 
Storage Batteries in Three- 
Wire System 500 

Storage Batteries. Variation 
of Electrolyte, Specific Grav- 
ity 146 

Storage Batteries, Zinc Acid. 140 



INDEX. 



759 



Storage Capacity 130 

Storage of Electric Quantity. 41 
Storage of Quantity of Elec- 
tricity, The 47 

Stray Field 184 

Strength "and Chemical Decom- 
position, Current 90 

Strength, Current 53 

Striking the Arc 535 

Subdivided Conductor, Induct- 
ance Reactance in 336 

Subscribers' Pole Connection. 717 
Sulphating, I'revention of . . . . 151 
Sulphuric and Nitric Acid De- 
polarizers 110 

Summary of Electro-Chemistry 90 
Summation of Alternating 

Quantities 342 

Sun Lamp. The 562 

Switchboard 445 

Switchboard Connections .... 712 

Switchboard. The Multiple... 706 

Switchboard. Operation of 708 

Switchboard Panels 445 

Switch Boxes and Circuit 

Breaker on Car 590 

Switches, Air 447 

Switches. Circuit Breakers as. 454 

Switches. Oil 447 

System, Anti-Parallel 488 

System for Arc Lamps, Fea- 
tures of Series or Constant- 
Current . . ; 475 

System, Closet 484 

System, Common Battery . . 697-698 

System, Constant-Current .... 472 

System, Constant-Potential . . 473 

System, Degree 321 

System, Five-and Seven-Wire. 502 

System, High-Voltage Parallel 503 

System, Lamp Signal 713 

System, Loop 483 

System, Multiple-Series 478 

System, Neutral Wii'e in Y. . . . 362 

System, Parallel-Circuit 554 

System. Potential Drop in Par- 
allel 482 

System, Rotary Converter in 

Three-Wire 393 

System, Series-Multiple 479 

System. Single-Dynaino Three- 
Wire 499 

System, Storage Batterv Equal- 
izer in Three- Wire 500, 501 

System, Telephone 692 

System, Three-Wire 497 

System, Tree 484 

System, Two-Dynamo Three- 
Wire 499 

Synchronous Motors. 

369, 373, 405, 436 

Table, Traction 588 

Tables, Winding 236 



Tamidine Filaments 523 

Tangent Galvanometer, The... 615 

Tangential Brushes 806 

Telegraphy, Wireless 733 

Telephone Circuit, Bridged.... 696 

Telephone Circuit. Series 695 

Telephone, Edison's 682 

Telephone as Galvanoscope, 

The 653 

Telephone Induction Coil, The. 684 
Telephone Induction Coil, Di- 
mensions of 686 

Telephone Induction Coil, Ef- 
fect of 688 

Telephone, Induction Coils in 

Bracket 688 

Telephone, Magneto, The 689 

Telephone Receiver a Dynamo. 212 
Telephone Receiver, Principle 

of 678 

Telephone Systems 692 

Telephone Transmitter. The . . . 079 
Temperature of Commutator . . 419 
Temperature of Dynamo or Mo- 
tor 439 

Temperature of Plating Baths 671 
Temperature. Standard Volt- 
age and Allowable 584 

Terminology of Analytical Ge- 
ometry 278 

Terrestrial Magnetism, Am- 
pere's Theory of 201 

Test for Cross Connections. 

Hand Magneto . . . . , 658 

Test For Ground, Hand Mag- 
neto 657 

Test, Rail-Joint 644 

Test of Resistance, Voltmeter 

and Ammeter 642 

Test, Varlev Loop 656 

Tests of Cable on Reels 652 

Tests, Engineering 658 

Tests, Galvanoscope Cable and 

Line 650 

Tests, Hand Magneto 656 

Tests. Impurities in Electrolyte 

and 155 

Tests, Line Insulation 643 

Tests, Line Resistance 643 

Tests, Polarity 404 

Theory of Magnetism, Am- 
pere's 200 

Theory of Terrestrial Magnet- 
ism, Ampere's 201 

Thomson or Kelvin Absolute 

Electrometer 617 

Thomsion or Kelvin Galvano- 
meter 609 

Thomson's Meter 515 

Threading, Interlinking and 

Cutting Lines of Force 205 

Three-Brush Dynamo 499 

Three-Phase Alternator Wind- 
ing, Six-Wire Connection of 359 



760 



ELECTRICIANS' HANDY BOOK. 



Three-Phase Cvirrent 347 

Three-Phase Induction Motor. 365 

Three-Phase Winding 358 

Three-Wire System 497 

Three-Wire System, Neutral 

Wire in 497-499 

Three-Wire System, Rotary 

Converter in 393 

Three - Wire System, Single- 
Dynamo 499 

Three-Wire System, Storage 

Batteries in 50(DI 

Three-Wire System, Storage 

Battery Equalizer in 501 

Three-Wire System, Two-Dyna- 
mo 499 

fThunder Clouds, Electromotive 

Force in 58 

Till Plating 668 

Torque 36 

Torque, Direct-Current Motor 

and 285 

Torque, Starting 367 

Total-Current Solenoid Amme- 
ter 467 

Traction Table 588 

Tractive Force of the Electro- 
Magnet 188 

Tractive Power, Electro-Mag- 
netic 192 

Transfer BusrBar 495 

Transformation, Ratio of 379 

Transformation, Step-Down 

and Step-Up 400 

Transformations, Algebraic... 18 
Transformer, Action of the . . . 383 
Transformer, Action of Motor. 400 
Transformer, Ammeter ...... 470 

Transformer, The Auto- 381 

Transformer. Choking of 376 

Transformer Construction, Ba- 
sis of 375 

Transformer, Construction of 

Rotary 391 

Transformer, The Limitation of 

a 377 

Transformer, Motor 400 

Transformer, Object of 376 

Transformer Practice, Motor. . 401 
Transformer, The Principle 

of a 377 

Transformer. Relations of Volt- 
age and Current in Rotary. 392 
Transformer, Use of Rotary . . 391 
Transformers, Breakdowns in. 437 

Transformers, Care of 437 

Transformers, Constant - Cur- 
rent 387 

Transformers, Core 380 

Transformers, Disk Winding of 387 
Transformers, Disk-Wound. . . . 380 
Transformers, Economy of Mo- 
tor = 401 

Transformers, Heat in 384 



Transformers, Individual 505 

Transformers, Inspection of. . . 438 
Transformers, Insulation for.. 390 
Transformers, Moisture in. . . . 438 

Transformers, Oil for 389 

Transformers, Oil for Filling. 437 
Trnnsform.ers, Operation of . . 396 
Ti'iinsformc-rs, Shell or Jacket 

Type 378, 379 

Transformers, Step-Up and 

Step-Down 378 

Transformers, Short Circuits 

in 438 

Translucent Scale for Galvano- 
meter 609 

Transmission of Signals, Wave 731 

Transmitter, The Blake 680 

Transmitter, Running 682 

Transmitter, Loose Carbon... 681 
Transmitter, The Solid Back. 683 
Transmitter, The Telephone.. 679 

Transmitting Apparatus 733 

Tree System 484 

Trigonometric F'unctions 33 

Tripping Platform 549 

Troubles, Motor 600 

Tudor Battery ISS 

Turns, Action of Demagnetiz- 
ing 269 

Turns, Ampere 176 

Turns of a Circuit and Induct- 
ance 334 

Turns, Dead 270 

Turns, Demagnetizing 268 

Turns, Increasing E.M.F. by 

Increasing 221 

Turns and Lines of Force, Re- 
lation between Ampere 183 

Twelve - Conductor Bipolar 

Armature 235 

Two-Dynamo Three-Wire Sys- 
tem 499 

Two-Phase Curren.t 346 

Two- Phase Operation 436 

Two-Phase Windings 357 

U-Shaped Electro-Magnets 189 

U-Shaped Magnets, Making. . . 196 
Underload Circuit Breaker .448-453 

Uniform Potential Methods... 492 

Unit of Quantity 45 

Units, Current and Rate 50 

Useful Constants 35 

Vacuum 527. 528 

Values, Average 327-328 

Values, Efeective 328-330 

Varley Loop Test 656 

Varying Field of Force 207 

Vector Diagram of Sine Curve 325 

Voice, The Human 678 

Voltage 62 

Voltage and Allowable Tem- 
perature, Standard 584 



index: 



761 



Voltage, Automatic Regulation 

of 492 

Voltage, Changing 400 

Voltage -Calculations 92 

Voltage and Current in Rotary 
Transformers, Relations of. 392 

Voltage Drop 536 

Voltage Drop and Arc Length 53S 
"\ oltages of Lamps, Individual 490 

Voltaic Arc, The 535 

Voltameter, Silver 90 

Volta's Pile 97 

Voltmeter, The 458 

Voltmeter and Ammeter Deter- 
mination of Resistance .... 642 

Voltmeter, Cardew's 463 

Voltmeter, Compensated 470 

Voltmeter, Empire 461 

Voltmeter, Measurement of Re- 

sistarce 642 

Voltmeter Scales, Graduation 

of 403 

Voltmeter, The . Stanley Hot- 
Wire 466 

Voltmeter, Weston's 459 

Voltmeters, General Notes on. 463 
Voltmeters, Hot-Wire 466 

Wadell-Entz Battery 140 

Wallace Lamp, The, 562 

Waste, Cotton 439 

Water Cooling 385 

Water Decomposed tav the Cou- 
lomb 88 

Wattless Current 246 

Wattmeter 470, 513 

Watts per Candle-Power in 

Arc Light 579 

Watts per Candle-Power in In- 
candescent Lamp 580 

Wave, The 316-318 

Wave Form, Influence of 544 

Wave and Frequency, Length 

of 319 

Wave and Lap Winding 238 

Wave Transmission of Signals 731 

Wave Winding 239 

Waves Produced by Electricity, 

Ether 50 

Wearing of Carbons 639 

Weights and Chemical Equiva- 
lents, Atomic 89 

Welding. Electric 728 

Weston's Voltmeter and Am- 
meter .' 459 

Wheatstone Bridge, or Bridge 

Box 632-634 

Wheels, Flat 597 

Wheels, Skiddirxg 598 



Wheels, Sliding 598 

Wire Ends in Cable, Finding. . 653 

Wire Gauges 85 

Wire, Idle 229 

Wire, Joints in Line 508 

Wire, Resistance 627 

Wire in Y System, Neutral... 362 

Wires for Bell Circuits 722 

Wires, Grounding 721 

Wives, Leading Bell 719-721 

Wires, Leading-in 526 

AVireless Telegraphy 733 

Wiring, Bell 718 

Wollaston's Battery 99 

Winding, Armature Polarity 

Due to 265 

Winding, Bipolar ...243, 244, 247 
Winding, Break in Armature . . 422 

Winding, Break in Field 430 

Winding Calculation, Example 

of Compound 259 

Winding and Commutator Bars, 

Bad Contacts between 419 

Winding, Compound, Long 

Shunt and Short Shunt. 256, 257 

Winding, Disk 357 

Winding, a Drum Armature, 

241-243, 246 
Winding of Dynamos, F'ield... 252 
Winding and Frame, Short 

Circuits betweeu Armature. 435 

Winding, Grouping of 350 

Winding, Insulation of 441 

Winding, Lap 238, 239, 249 

Winding, Multipolar, 

237, 245, 246, 315 
Winding, Principle of Alter- 
nating-Current Armature . . . 350 

Winding, Series 252-254 

Winding, Short Circuits in 

Field 430 

Winding, Shunt 254,255 

Winding, Six-Wire Connection 

of Three-Phase Alternator . . 359 

Winding, Three-Phase 358 

Winding Tables 236 

Winding, Two-Phase 357 

Winding, Wave 238, 239 

Windings of Stator, Local 

Heating of 436 

Y Connections for Alternating- 
Current 506 

Y or Star Connection 359 

Y System, Neutral Wire in... 362 

Zamboni's Pile . . 99 

Zinc Acid Starag3 Batteries. . 140 



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SLOAIVE. How to Become a Successful Electrician. 

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SIvOANE. Arithmetic of Electricity. 

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SLOANE. Electrician's Handy Book. 

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SLOANE. Ruhher Hand Stamps and the Manipulation of Ruhber. 

A practical treatise on the manufacture of all kinds of rubber 
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SliOANE. Electric Toy 3Iakiugr> Dynamo Building, and Electric 
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SL.OANE. Liquid Air and the Liquefaction of Ga.se8. 

Containing the full theory of the subject and giving the 
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SLOANE. Standard Electrical Dictionary. 

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USHER. The Modern Machinist. 

A practical treatise embracing the most approved methods of 
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A new book from cover to cover. Fifth edition. 257 engravings. . 
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VAN DERVOORT. American Lathe Practice. 

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VAIV DERVOORT. 3Iodern Machine Shop Tools; Their Construc- 
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This is a book of reference that will be found convenient 
in every machine shop. Suppose it is desired to know how to 
cut bevel gears, to calculate milling machine spirals or to make 
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hole drilling; turning tapers; testing lathes, etc.; or any one 
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'SVALLIS - TAYLOR. Pocket Book of Refrigeration and lee 
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This explains the properties and refrigerating effect of the 
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reference by refrigerating- engineers, with nearly one hundred 
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WOOD^VORTH. American Tool Makiiig and I'ntercban^eable 
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A complete treatise on the Art of American Tool Making and 
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WOODWORTH. Dies, Their Construction and Use for tlie Modern 
Working of Slieet Metals. 

A practical work on the designing, constructing and use of 
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production of sheet metal parts and articles. Comprising funda- 
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WOODWORTH. Hardening, Tempering, Annealing and Forging 
of Steel. 

A new book containing special directions for the successful 
hardening and tempering of all steel tools. Milling cutters, taps, 
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the simplest and most satisfactory hardening and tempering pro- 
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steel may be adapted are concisely presented, and their treatment 
for working under different conditions explained, as are also the 
special methods for the hardening and tempering of special 
brands. 320 pages. 250 illustrations. $2.50. 
WRIGHT. Electric Furnaces and Tlieir Industrial Applications. 

Contains 285 pages, and 57 illustrations, which are essentially 
in the nature of sectional diagrams, representing principles of 
construction. This is a timely and practical treatise on the forms 
and uses of electric furnaces in modern electro-chemical pro- 
cesses. Price, $3.00. 



JUL 10 1913 



jsmmmmm 



1 



